70  / 


AVIATION 

ENGINES 


JOHN   C,  CHADWFCK 
LIEUT.  (J.G.)  U,S.N,  R,P 


UC-NRLF 


E77    137 


IMC, 


NEW  YOHK, 


AVIATION  ENGINES 


JOHN  C.  CHADWICK 

LIEUTENANT  (J.G.)  U.  S.  N.  R.  F. 


Published  by  Authority  of  the  Secretary  of  the  Navy 


PUBLISHED  BY 
EDWIN  N.  APPLETON,  INC. 

ONE  BROADWAY 
NEW    YORK    CITY 


/ 


COPYRIGHT,   1919 

BY 
EDWIN  N.  APPLETON,  INC. 


'"THE  author  wishes  to  express  his  thanks  and  appreciation 
to  the  following  concerns  who  furnished  photographs  and 
other  material  making  possible  the  writing  of  this  book: 

The  Zenith  Carburetor  Co.,  Detroit,  Mich. 

The  Packard  Motor  Car  Co.,  Detroit,  Mich. 

The  Curtiss  Aeroplane  and  Motor  Corp.,  Garden  City,  L.  I. 

The  Manufacturers'  Aircraft  Association,  New  York  City. 


416880 


CONTENTS 


PAGE 

Introductory    9 

Nomenclature    10 

Definitions    14 

Principle  of  Operation  of  a  Four-Stroke  Cycle  Engine 15 

Valve   Location 17 

Propeller  Drive    18 

Multi-Cylinder  Arrangement   20 

Cooling    22 

Radiators    22 

Water  Circulation   22 

Water  Pumps  23 

Operation  of  Cooling  System 23 

Lubrication    24 

Carburetion    26 

Effects  of  Improper  Carburetion 33 

Electricity  and  Magnetism 35 

Induction 35 

Ignition    36 

Magnetos    41 

Dixie   Magneto    42 

Timing   44 

Emergency  Repairs  49 

Engine  Characteristics 

Liberty    51 

Liberty-Delco   Ignition   System 62 

Order  of  Teardown— U.  S.  N.  Liberty  Motor  School...  72 

Teardown— U.  S.  N.  Liberty  Motor  School 73 

Hispano  Suiza    79 

Curtiss— Model   OXX6    83 

Materials  of   Construction 86 

Trouble  Charts  .  .  88 


PREFACE 

IN    writing   this    book    the    author    has    endeavored   to    set 
forth  the  underlying  principles  of  the  Internal  Combustion 
Engine  as  used  in  Aviation.     The  actual  engines  discussed 
are  those  that  were  used  most  widely  by  the   United  States 
Naval  Aviation  Corps  during  the  recent  war.     They  may  be 
taken  as  very  representative  and  highly  efficient  engines  cover- 
ing the  field  of  American  aviation  in  general  at  the  present 
time.     The  Rotary  Engine  is  not  discussed,  since  its  use  was 
discontinued  by  our  Navy,  although  it  was  widely  used  in  light 
foreign  planes,  particularly  those  of  French  design. 

The  author  has  endeavored  to  set  forth  in  non-technical 
language  and  without  the  use  of  mathematics,  the  main  features 
of  the  principles  employed  in  any  internal  combustion  gasoline 
engine,  and  show  their  adaptation,  in  the  three  engines  speci- 
fically discussed :  the  Liberty,  Curtiss  model  OXX,  and  Hispano 
Suiza. 

The  purpose  of  this  book  is  to  give  anyone  desiring  to 
operate  an  airplane,  a  fundamental  understanding  of  engines  as 
used.  It  is  founded  on  the  course  of  instructions  as  given  at 
the  U.  S.  Naval  Aviation  Detachment,  Massachusetts  Institute 
of  Technology,  in  Training  Pilots  for  service.  It  is  not  intended 
for  purposes  of  design,  criticism  or  recommendation,  but  simply 
for  instruction  of  the  average  individual,  assuming  he  knows 
nothing  of  a  gas  engine. 

For  books  pertaining  to  the  mathematics  of  design,  the 
author  recommends: 

Judges — "High  Speed  Internal  Combustion  Engines." 
"The  Gasoline  Motor,"  by  P.  M.  Heldt. 


AVIATION   ENICINES 


INTRODUCTORY 

Engines  used  in  Aviation  are  all  of  the  internal  combustion 
type.  By  internal  combustion  is  meant  that  the  combustion  or 
burning  of  the  fuel  takes  place  in  the  engine  itself.  The  fuel 
used  is  gasoline  (hydro  carbon),  and  when  mixed  with  air 
becomes  highly  explosive. 

The  mechanical  parts  of  the  engine  consist  of  a  cylinder, 
piston,  connecting  rod  and  crank  shaft.  The  explosive  mixture 
is  drawn  into  the  cylinder,  one  end  of  which  is  closed  by  the 
cylinder  head,  and  the  other  end  plugged  by  the  piston.  The 
explosive  mixture  is  ignited  by  an  electric  spark  and  the  ex- 
pansion of  the  burning  charge  causes  the  piston  to  move  down 
in  the  cylinder,  just  as  the  charge  of  powder  in  a  gun  causes 
the  projectile  to  move  down  the  barrel  of  the  gun.  As  the 
motion  desired  to  turn  a  propeller  (which  is  used  for  the  pro- 
pulsion of  the  aeroplane)  is  rotary,  the  travel  of  the  piston  is 
converted  into  rotary  motion  by  connecting  the  piston  to  a 
crank  shaft,  with  a  connecting  rod.  The  motion  of  the  piston 
then  becomes  reciprocating,  up  and  down  in  the  cylinder. 

An  internal  combustion  engine  is,  therefore,  an  engine  that 
obtains  its  power  from  the  rapid  combustion  and  consequent 
expansion  of  some  inflammable  gas;  and  must  have,  in  addition 
to  the  parts  named  above,  ports  and  valves,  whose  opening  and 
closing  are  so  controlled  as  to  admit  the  explosive  gas  into,  the 
cylinder  and  to  expel  the  burnt  gas.  The  degree  of  heat  gen- 
erated by  the  explosion  of  a  charge  is  extremely  high — in  fact 
higher  from  the  melting  point  of  some  metals,  and  it  can 

9 


therefore- lbe  seen:  t  *K&  continued  series  of  explosions  would 
SOQYI  c^u&e4;he^eK£lne,to,  become  heated  to  such  an  extent  that 
it  ^couki\Lnt)t  ^pe'r^o  It,  is  .therefore  necessary  to  keep  the 
temperature  of  the  engine  within  safe  working  limits,  and  for 
this  purpose  a  cooling  system  becomes  necessary.  The  engine 
must  be  very  carefully  oiled,  and  for  this  purpose  a  lubricating 
system  is  necessary.  As  the  fuel  used  is  hydro  carbon,  a  device 
must  be  used  to  convert  the  hydro  carbon  into  a  combustible 
gas.  The  device  is  called  a  carburetor  and  is  referred  to  as 
the  carburetion  system.  After  the  gas  had  been  introduced 
into  a  cylinder,  some  means  for  igniting  it  must  be  provided  in 
order  that  it  may  explode.  This  apparatus  is  called  the  igni- 
tion system.  It  can  be  seen  from  the  above  that  there  are  four 
systems  that  are  absolutely  necessary  in  the  construction  of  an 
internal  combustion  engine. 

NOMENCLATURE 

There  are  of  course  a  great  many  parts  to  an  engine 
besides  those  mentioned  or  alluded  to  in  the  introductory.  The 
names  of  the  various  parts  are  in  the  most  part  self-explana- 
tory. 

It  has  been  shown  that  it  is  necessary  to  have  a  cylinder 
in  which  the  explosion  and  expansion  of  gases  may  take  place, 
and  in  which  the  piston  may  travel. 

It  is  necessary  to  have  an  intake  valve  and  port  so  that 
incoming  gases  may  be  admitted  properly  to  the  cylinder.  This 
makes  necessary  an  intake  manifold,  or  pipe,  for  conducting 
the  gases  from  the  carburetor  to  the  intake  port.  Likewise  it 
is  necessary  to  have  an  exhaust  valve  and  port,  and  in  many 
cases  an  exhaust  manifold  to  carry  away  the  exhaust  gases. 

The  piston  must  then  be  fastened  to  the  connecting  rod. 
This  is  done  by  means  of  the  piston  pin  and,  in  order  that  steel 
may  not  meet  steel,  a  fine  bronze  or  brass  sleeve  is  placed  in- 
side the  hole  of  the  upper  end  of  the  connecting  rod.  This  is 

10 


known  as  a  bushing.  The  lower,  or  big  end  of  the  connecting 
rod,  is  then  fastened  to  the  crank  shaft.  Again  so  that  steel 
surfaces  will  not  be  in  contact  a  bearing  of  softer  metal  is 
used.  In  this  case,  for  ease  of  assembly  and  because  of  the 
larger  surface,  a  bronze  or  brass  shell,  which  is  split,  is  lined 
with  babbit  or  white  metal  and  provides  the  rubbing  surface. 
This  is  known  as  the  connecting  rod  bearing. 

The  crank  shaft  is  the  revolving  part  of  the  engine  and 
consequently  it  must  be  supported.  This  is  done  by  means  of 
bearings  placed  in  webbing  of  the  crank  base,  and  these  bear- 
ings are  known  as  main  bearings.  The  crank  shaft  receives  its 
power  from  the  piston  and  connecting  rod.  Consequently  it 
must  have  offsets  or  throws  so  that  the  heretofore  straight  line 
motion  may  become  rotary.  The  part  of  the  crank  shaft  which 
rests  in  the  main  bearings  is  known  as  the  journal.  The  part 
to  which  the  connecting  rod  is  attached  is  called  the  crank 
pin  and  the  parts  connecting  the  two  are  called  the  cheeks. 

Now  it  is  necessary  to  have  the  valves  actuated  at  the 
proper  moments.  This  is  done  primarily  by  means  of  the  cam 
shaft.  This  is  a  shaft  upon  which  cams  or  eccentrics  are 
placed.  The  shaft  revolves,  being  geared  to  the  crank  shaft. 
Then  when  the  high  part  or  toe  of  the  cam  hits  the  lever  or 
valve  actuating  mechanism,  the  valve  is  forced  off  its  seat  and 
remains  open  as  long  as  the  high  point  of  the  cam  stays  in 
position.  The  valve  is  opened  always  against  the  action  of  a 
spring,  which  closes  it  as  soon  as  the  cam  is  in  a  position  to 
permit. 

Following  is  a  summary  of  the  important  parts  of  an 
engine.  A  glance  at  the  accompanying  cuts  \vill  show  their 
assembly  and  co-ordination. 

Cylinder:  That  part  of  the  engine  in  which  combustion  and 
expansion  occurs;  and  in  which  the  piston  reciprocates. 

Valves  and  Valve  Ports:  Located  in  cylinder  head  to  allow 
control  of  incoming:  and  exhaust  gases. 

11 


End  View 


Cross  Sections. 


A-   CYLINDER 

S-  PISTON 

C  -CONNECTING     ROD 

D-CRAMK   PIN 

F-MAIIN    BEARING 
G-  THRUST        i. 
H-CRANK   CASE 
I  -   SUMP 
J-  CAM   SHAFT 


K-  ROCKS  R 

L-  VALVE     SPRING 


N  -  C 

O-  WATER    JACKET 

P-  PISTON  PIN 

<J-  VALVE  , 

M-  CRANK    SHAFT 

S-  WATER   MANIFOLD   CONNECTFOf 


12 


A — Cylinder.  D — Rocker   Arms.       F — Valve   Springs. 

B— Valves.  E— Valve  P^rts.          H— Cam. 

I_\Vater  Jackets.  J— Valve  Clearance. 


13 


Piston:  That  part  upon  which  expansion  acts,  causing 
downward  action. 

Connecting  Rod:  Connects  piston  to  crank  shaft,  thereby 
converting  reciprocating  motion  into  rotary  motion. 

Crank  Shaft:  That  member  which  receives  rotary  motion 
from  the  connecting  rods  and  transmits  it  to  the  propeller 
either  direct  or  through  gearing. 

Crank  Case:  Housing  which  furnishes  a  means  of  support 
for  the  crank  shaft  and  cylinder. 

Sump:  Lower  part  or  apron  for  the  crank  case,  deriving 
its  name  from  the  fact  that  it  is  very  often  the  oil  reservoir. 

Cam  Shaft:   Prime  mover  for  the  valve  operation. 

Timing  Gears:  Gears  by  means  of  which  the  proper  speed 
of  rotation  is  transmitted  from  the  crank  shaft  to  the  cam 
shaft. 

Rocker  Arm:  Lever  mechanism  for  opening  the  valve. 

Valve  Spring:   Spring  for  closing  the  valve. 

Intake  Manifold:  Pipe  or  passage  through  which  gases 
are  drawn  into  cylinder. 

Water  Manifolds:  Pipes  through  which  water  is  distrib- 
uted to  and  from  cylinders. 

Thrust  Bearing:  A  ball-bearing  that  receives  the  push  or 
pull  of  the  propeller. 

DEFINITIONS 

Cycle  of  Operations:  Series  of  events  which  occur  in  an 
engine  from  one  intake  stroke  to  the  next. 

Top  Dead  Center:  Uppermost  point  of  piston  travel. 

Bottom  Dead  Center:  Lowermost  point  of  piston  travel. 

Bore:   Inside  diameter  of  cylinder. 

Stroke:  Distance  travelled  by  piston  from  top  to  bottom 
dead  centers. 

Piston  Displacement:  Generally  referred  to  as  meaning 
the  total  piston  displacement  of  an  engine,  which  is  the  volume 

14 


of  the  space  displaced  by  the  piston  in  one  stroke  times  the 
number  of  cylinders. 

Back  Fire:  Pop  back  or  explosion  in  intake  manifold  or 
carburetor.  Caused  by  improperly  seated  intake  valve  or  mix- 
ture too  lean.  Causes  a  great  many  engines  to  catch  fire  and 
is  a  dangerous  condition. 

Back  Kick:  Rotation  of  .the  engine  in  wrong  direction, 
caused  by  pre-ignition,  or  spark  advanced  too  far.  Dangerous 
especially  when  cranking  by  hand. 

After  Firing:  Is  the  engine  running  after  the  switch  has 
been  cut,  and  is  due  to  carbon  particles  in  the  combustion 
chamber  or  overheating.  All  aviation  engines  will  continue 
to  run  after  the  switch  has  been  cut  unless  they  are  allowed  to 
run  slowly  for  a  few  minutes  and  cool.  After  firing  is  very 
injurious  to  the  engine  and  very  often  results  in  the  breaking 
of  timing  gears,  and  other  parts. 

Idling:  When  an  engine  is  running  at  a  low  speed  (200 
r.p.m.  to  800  r.p.m.,  according  to  the  make  of  engine)  it  is  said 
to  be  idling. 

Contact:  Ignition  switches  in  the  starting  position,  throttle 
nearly  closed  ready  for  starting. 

Off:   Ignition  switch  in  off  position. 

Throttle  open:  Throttle  controls  in  wide  open  position,  for 
purpose  of  drawing  in  a  charge  of  gas  for  starting. 

Spark  retarded:   Spark  controls  at  point  of  extreme  retard. 

PRINCIPLE  OF  OPERATION  OF  A  FOUR- 
STROKE  CYCLE  ENGINE 

It  has  already  been  mentioned  that  power  is  obtained  from 
the  explosion  and  consequent  expansion  of  a  gas,  which  is  the 
mixture  of  gasoline  and  air.  Obviously  it  is  necessary  to  clean 
the  burned  gas  out  of  the  cylinder  when  its  power  has  been 
utilized.  Also  it  is  necessary  to  admit  and  draw  a  new  charge 
into  the  cylinder. 

15 


There  also  is  another  important  matter  to  be  considered, 
namely,  that  all  possible  power  must  be  obtained  from  the  ex^ 
panding  gas.  It  has  been  found  that  by  compressing  a  charge 
before  igniting  it  the  power  derived  will  be  vastly  increased.; 
Consequently  there  is  still  another  item  to  be  considered  and 
which  must  be  performed  in  the  cylinder,  vk. :  compression. 

From  the  foregoing  it  can  be  seen  that  it  is  necessary  to  go< 
through  four  distinct  operations  to  obtain  one  power  impulse.! 
Gas  must  be  taken  in;  this  gas  must  be  compressed;  power  o| 
work  can  then  be  derived  from  the  ignition  and  expansion  o; 
the  gas;  and  then  the  burned  gases  must  be  expelled. 

All  of  these  operations  in  a  four-stroke  cycle  engine  an 

performed  by  four  strokes  of  the  piston.     Bearing  in  mind  tin 

fact  that  the  piston  is  attached  to  the  crank  shaft  by  the  con^ 

necting  rod  it  will  be  seen  that  the  crank  shaft  consequent!' ' 

makes  two  revolutions  in  this  time.     The  four  strokes  nece:' 

sary  to  complete  one  cycle  then  are : 

1— Intake, 

2 — Compression, 

3 — Power, 

A — Exhaust. 

Consequently  there  is  but  one  impulse  per  cylinder  to  every 
two  revolutions  of  the  crank  shaft.  Practically  all  aviation 
engines  used  at  present  operate  upon  this  principle. 

It  may  be  noted  here  also  that  there  is  a  point  of  upper- 
most travel  and  a  point  of  lowermost  travel  for  the  piston  at 
the  beginning  and  end  of  each  stroke.     The  uppermost  point 
is  known  as  Top  Dead  Center  or  just  Top  Center.     Likewise  j 
the  lowermost  is  Bottom  Dead  Center  or  Bottom  Center. 

The  cycle  of  operations  begins  with  the  piston  in  the 
uppermost  position  in  the  cylinder.  At  this  point  a  valve  put- 
ting the  cylinder  in  communication  with  the  carburetor  opens. 
The  piston  then  travels  down  in  the  cylinder  drawing  in  a  ] 
charge  of  gas  from  the  carburetor.  When  the  piston  reaches 
the  end  of  its  downward  stroke,  the  valve  closes;  the  cylinder 


is  then  closed  and  the  piston  on  the  following  up  stroke  com- 
presses the  charge  and,  at  approximately  top  center,  a  spark 
occurs  in  the  cylinder,  igniting  the  charge;  the  piston  is  then 
subjected  to  the  pressure  of  the  burning,  expanding  gas,  and  is 
forced  down  in  the  cylinder;  this  is  the  power  stroke.  At  the 
end  of  the  power  stroke  the  piston  is  again  at  bottom  center. 
At  approximately  the  end  of  the  power  stroke,  another  valve 
opens  a  port  communicating  with  the  atmosphere,  and  the  pis- 
ton on  the  next  up  stroke  forces  the  burnt  gas  out  of  the  cylinder, 
and  this  valve  closes  at  approximately  top  center.  The  engine 
has  then  completed  one  cycle  and  is  ready  for  the  next. 

Beginning  with  the  piston  at  top  center,  the  cycle  of 
events,  piston  and  valve  movements  can  be  followed  thus: 

Event  Piston  Stroke          Position  of  Valves 

1.  Intake  1.  Down  Intake  valve  open 

2.  Compression  2.  Up.  Both  valves  closed 

3.  Power  3.  Down  Both  valves  closed 

4.  Exhaust  4.  Up  Exhaust  valve  open 

VALVE  LOCATION 

Valve  location  has  a  great  deal  to  do  with  the  power  output 
of  an  engine.  In  early  practice,  valves  were  located  in  pockets 
at  the  side  of  the  cylinder  head  proper.  Cylinders  of  this  char- 
acter come  under  two  main  headings.  Where  the  exhaust  valve 
is  on  one  side  and  the  intake  on  the  opposite  side  the  cylinder 
is  termed  "T"  head.  Where  the  exhaust  and  intake  valves  are 
both  on  the  same  side,  the  cylinder  is  termed  "L"  head.  Both 
the  above  types  have  disadvantages  because  of  the  pocket  for- 
mation, which  hinders  scavenging  and  power  development.  In 
the  above  cases  the  valves  are  operated  by  simple  adjustable 
lifters  transmitting  the  cam  action  to  the  valve  stems. 

In  later  practice  the  "L"  head  and  "T"  head  have  practi- 
cally given  way  to  the  "I"  head,  in  which  the  two  halves  are 
located  directly  in  the  head  of  the  cylinder  proner  and  operate 

17 


downward.  In  this  type  of  cylinder  the  valves  are  operated  by 
means  of  an  overhead  cam  shaft  with  rocker  arms;  or  if  the 
cam  shaft  be  located  in  the  crank  case,  by  means  of  a  system 
of  pushrods  and  rocker  arms. 

A  rocker  arm  is"  simply  a  lever,  pivoted  near  the  middle, 
one  end  riding  on  the  cam  surface  and  transmitting  the  cam 
action  to  the  valve  stem  by  means  of  the  other  end.  The  part 
which  comes  in  contact  with  the  valve  stem  is  called  the  tap- 
pet. It  is  usually  in  the  form  of  a  small  bolt  so  that  it  may  be 
adjustable.  This  is  necessary  to  give  valve  clearance  or  a 
clearance  between  the  valve  stem  and  the  tappet.  Valves  are 
subjected  to  high  temperatures  and  therefore  must  expand.  It 
is  necessary  to  allow  for  this  expansion.  If  no  valve  clearance 
were  allowed  expansion  would  take  place  and  the  valve  would 
be  held  open,  or  off  its  seat,  too  long  or  all  altogether.  This 
would  result  in  loss  of  compression  and  consequent  loss  of 
power.  It  may  then  be  seen  that  valve  clearance  is  very 
important  and  must  be  kept  adjusted.  Valve  clearances  differ 
with  various  engines,  but  are  always  specified  by  the  manu- 
facturer. Usually  the  exhaust  valve  clearance  will  be  the 
greater  since  this  valve  is  subjected  to  greater  heat  than  is  the 
intake.  It  is  just  as  important  for  proper  operation  not  to 
have  too  much  valve  clearance  since  this  would  allow  the  valve 
to  open  late  and  close  early.. 

To  insure  against  loss  of  compression  the  valve  must  make 
a  gas-tight  fit  on  its  seat.  To  accomplish  this,  valves  are 
"ground  in,"  using  a  grinding  compound  of  emery  or  some 
hard  substance,  so  that  the  seat  on  both  valve  and  port  will  be 
symmetrical  and  perfectly  smooth. 

PROPELLER  DRIVE 

The  method  of  driving  the  propeller  depends  upon  the 
running  speed  of  the  engine.  The  speed  at  which  the  propeller 
may  efficiently  be  driven  is  limited  to  a  rather  narrow  range, 

18 


varying  ordinarily  from  1100  to  1500  r.p.m.  It  has,  however, 
been  found  practical  to  operate  especially  designed  and  con- 
structed propellers  at  speeds  as  high  as  1800  r.p.m.  This,  how- 
ever, is  done  at  some  sacrifice  to  efficiency.  The  enormous 
centrifugal  force  developed  by  high  speed  rotation  is  of  course 
one  of  the  main  limiting  factors,  but  the  even  more  serious  one 
is  the  slippage  and  consequent  efficiency  drop  occurring  at  high 
speeds.  Where  the  engine  speeds  remain  below  1600  to  1800 
r.p.m.  the  propeller  will  usually  be  driven  by  direct  attachment 
to  the  crank  shaft  itself,  by  means  of  a  hub,  keyed  or  shrunk  on 
and  secured  by  lock  nuts. 

There  is,  however,  a  constantly  increasing  tendency  toward 
engines  of  higher  speeds  in  order  to  take  advantage  of  the 
consequent  reduction  in  weight  per  horse-power  developed. 
The  output  naturally  is  augmented  as  the  speed  increases  and 
if  the  weight  of  the  engine  can  be  maintained  about  constant, 
or  only  slightly  increasing,  the  advantage  is  readily  apparent. 
This  tendency  is  becoming  more  and  more  prevalent  and 
makes  necessary  the  geared  down  propeller  drive.  By  employ- 
ing a  propeller  drive  shaft  geared  to  the  crank  shaft,  it  is 
perfectly  possible  to  surmount  the  difficulty  and  maintain  effi- 
cient propeller  speeds  by  properly  regulating  the  gearing.  At 
the  present  time  gearing  has  been  so  greatly  improved  that  the 
consequent  drop  in  horse-power  output,  through  its  employ- 
ment, is  practically  negligible  as  is  the  consequent  increase  of 
weight  which  it  causes. 

The  thrust  of  the  propeller  is  transmitted  through  the 
engine  to  the  longerons  of  the  fuselage.  It  is  taken  up  by  the 
crank  case  from  the  crank  shaft  by  a  ball  thrust  bearing  at  the 
propeller  end  of  the  shaft. 

It  is  most  important  to  keep  the  propeller  lined  up  at  all 
times,  otherwise  severe  and  dangerous  vibration  will  result. 
The  most  common  method  of  checking  propeller  allignment  is 
to  measure  from  a  fixed  point  on  the  engine  to  a  certain  point 

19 


on  the  propeller  surface,  the  propeller  blade  being  in  the  ver- 
tical position.  Bring  the  other  blade  into  the  same  position 
and  measure  the  corresponding  distance.  This  should  check 
within  1/32"  to  1/16".  If  the  error  is  greater  it  can  be  coun- 
teracted by  means  of  the  hub  bolts.  If  propeller  vibration  is 
noticed  and  lining  does  not  correct  it,  change  the  propeller,  as 
propellers  have  been  known  to  be  inherently  wrong  and  yet 
appear  to  be  as  specified  in  every  way. 

MULTI-CYLINDER  ARRANGEMENT 

From  the  events  of  the  four-stroke  cycle  it  will  be  seen 
that  there  is  only  one  power  application  on  a  piston  during  the 
four  strokes.  In  other  words,  the  power  stroke  must  furnish 
energy  enough  to  carry  the  engine  through  three  dead  strokes 
and  also  to  perform  useful  work.  Realizing  this,  it  is  simple 
to  see  that  the  one  cylinder  engine  will  deliver  power  in  a 
very  spasmodic  manner. 

It  would  be  perfectly  possible  to  build  a  one-cylinder 
motor  of  enormous  horse-power,  but  the  explosions  would  be 
so  tremendous  and  occurring  at  such  a  distance  apart,  that  not 
only  would  the  engine  have  to  be  enormously  heavy,  but  vibra- 
tion would  be  such  that  it  would  be  utterly  useless. 

One  great  advantage  of  the  electric  motor  is  that  power  is 
applied  to  the  rotating  shaft  throughout  its  entire  rotation. 
Then  why  not  break  up  the  dead  intervals  of  the  one-cylinder 
engine  by  utilizing  several  cylinders  whose  combined  power 
would  approach  a  steady  application  instead  of  coming  spas- 
modically? This  would  have  numerous  advantages.  Compar- 
ing a  one-cylinder  engine  to  an  engine  of  several  cylinders,  but 
the  same  horse-power,  it  is  easily  seen  that  the  power  delivery 
will  be  more  constant,  and  terrific  strains  will  be  eliminated, 
due  to  the  more  constant  succession  of  power  strokes.  This 
means  that  vibration  will  be  reduced,  weight  of  parts  will  be 

20 


reduced  and  consequently   internal   friction,   all   of  which  will 
tend  to  increase  the  useful  work  output  of  the  engine. 

With  these  thoughts  in  mind,  it  is  clear  why  the  one- 
cylinder  arrangement  gave  way  to  the  two,  and  the  two  to  the 
four  and  six,  and  the  four  and  six  to  the  eight  and  twelve. 
For  naval  aviation  purposes  four  cylinders  is  the  minimum 
number  used.  Where  fours  and  sixes  are  used  the  cylinders 
are  arranged  vertically  in  a  straight  line  and  a  crank  shaft 
constructed  so  that  connecting  rods  from  each  cylinder  may 
be  attached  to  each  crank  throw.  In  these  engines  the  crank 
shafts  have  as  many  throws  as  there  are  cylinders  and  are  so 
constructed  that  power  is  applied  evenly  throughout  each  revo- 
lution. 

If  eight  cylinders  are  to  be  used  it  is  obvious  that  their 
arrangement,  vertically  in  a  straight  line,  would  necessitate  a 
very  long  crank  shaft,  and  the  engine  would  take  up  great 
space.  It  is  possible  to  obviate  this  by  splitting  the  cylinders 
into  two  sets  and  placing  these  sets,  or  banks  as  they  are  com- 
monly termed,  on  an  angle  with  each  other.  Such  an  engine 
is  called  an  eight-cylinder  V-type  engine  because  of  the  V  angle 
between  banks.  With  this  arrangement  it  is  then  seen  that  the 
space  occupied  is  much  more  compact.  Also  the  necessity  of  a 
very  long  crank  shaft  is  overcome,  and  by  regulating  the  angle 
between  banks,  the  ordinary  four-cylinder  crank  shaft  is  used, 
having  t\vo  connecting  rods,  one  from  each  bank,  fastened  to 
each  crank  pin.  The  same  principles  are  applied  to  the  twelve 
cylinder  engines,  except  that  the  banks  consist  of  six  cylinders 
each  and  again,  by  regulating  the  angle  between  banks,  the 
six-cylinder  crank  shaft  is  used.  The  regulation  of  this  angle 
depends  upon  the  firing  interval  desired.  If  the  interval  is  to 
be  equal,  the  angle  between  banks  must  equal  the  firing  interval. 
If  the  angle  is  of  any  other  value  the  firing  intervals  will  be 
unequal. 


21 


COOLING 

The  combustion  of  the  explosive  mixture  inside  the  cylin- 
der of  an  aviation  engine  generates  intense  heat;  this  con- 
tinued generation  of  heat  would  soon  render  the  engine  inop- 
erative if  the  cylinders  were  not  cooled  in  some  way.  There 
are  two  ways  of  doing  this,  with  air  or  with  water.  The  prin- 
ciple of  both  systems  is  to  conduct  the  excess  heat  of  combus- 
tion rapidly  enough  away  from  the  cylinder  walls  to  prevent 
damage  by  burning  away  the  oil  and  causing  the  pistons  to 
seize. 

Water  Cooling:  Heat  is  dissipated  in  a  water-cooled 
engine  by  surrounding  the  cylinder  wall  with  another  wall,  and 
by  circulating  water  through  the  space  in  between  the  two. 
The  external  wall  is  called  the  water  jacket.  Water  jackets 
around  the  cylinders  can  be  formed  in  various  ways.  If  the 
cylinders  are  of  cast  iron  or  cast  aluminum,  the  jacket  is 
usually  cast  integral  with  the  cylinder.  Sometimes  the  jacket 
is  made  of  sheet  metal,  brazed  or  welded  to  the  cylinder.  This 
latter  type  of  jacket  is  used  when  the  cylinders  are  of  steel,  as 
in  the  Liberty  engine.  Only  a  small  quantity  of  water  can  be 
carried  in  an  airplane,  hence  the  hot  water  which  has  just  cooled 
the  cylinder  must  itself  be  cooled  and  used  over  again. 

RADIATORS 

The  hot  water  from  the  water  jacket  is  cooled  by  air  in 
much  the  same  manner  as  an  air-cooled  engine  cylinder,  that 
is,  by  radiation  and  conduction.  The  device  for  this  purpose 
is  called  a  radiator,  and  consists  of  a  series  of  very  thin  water 
passages  around  which  air  can  circulate.  Circulation  of  air  is 
provided  by  the  motion  of  the  plane  through  the  air. 

WATER  CIRCULATION 

The  water,  in  being  used  over  again,  is  circulated  through 
the  water  jacket  and  then  through  the  radiator.  The  direction 

.    22 


of  circulation  is  determined  by  the  fact  that  heated  water  tends 
to  rise  and  cooled  water  to  fall.  Hence,  the  cooled  water  from 
the  radiator  is  introduced  at  the  bottom  of  the  water  jacket, 
and  the  hot  water  from  the  top  of  the  water  jacket  is  led  off  to 
the  top  of  the  radiator.  This  natural  tendency  for  heated 
water  to  rise  is  sufficiently  strong  to  cause  an  actual  circula- 
tion of  water  around  the  cooling  system,  provided  the  water 
passages  are  large,  and  the  system  full  of  water.  This  is  called 
thermo-syphon  circulation.  It  is  customary  on  aviation  en- 
gines, however,  to  make  the  water  circulation  positive  by 
means  of  a  pump  acting  in  the  direction  of  the  thermo-syphon 
action.  By  this  means  less  \vater  is  required  and  the  cylinder 
temperature  can  be  more  closely  controlled. 

WATER  PUMPS 

The  kind  of  water  pump  most  commonly  used  is  the  centri- 
fugal type,  consisting  of  a  rotating  impeller  or  paddle  wheel 
in  a  casing.  Water  is  led  into  the  center  of  the  impeller  and 
is  thrown  out  to  the  edge  by  centrifugal  force.  The  outlet  is 
at  the  rim  of  the  casing. 

OPERATION  OF  COOLING  SYSTEM 

The  temperature  of  the  water  in  the  cooling  system  is  an 
excellent  indication  of  the  condition  of  the  cooling,  lubrication, 
carburetion  and  ignition  systems,  as  there  are  troubles  which 
can  occur  in  all  these  systems  which  cause  overheating. 
Hence  a  thermometer  of  some  kind  with  a  dial  on  the  cockpit 
instrument  board  is  used  to  indicate  the  water  temperature. 
Excessive  water  temperature  should  lead  to  an  investigation 
of  its  cause. 

It  is  impossible  to  lay  too  much  stress  upon  the  importance 
of  this  instrument.  It  is  the  pulse  of  the  cooling  system.  The 
pilot  must  be  familiar  with  its  proper  recordings  and  should 
train  himself  to  pay  particular  attention  to  it  at  all  times.  If 

23 


this  is  done  trouble  may  very  probably  be  remedied  before  it 
becomes  dangerous.  The  bulb  of  the  water  temperature  meter 
is  usually  located  in  the  outlet  header  of  the  water  system,  and 
indicates  thr  temperature  of  the  water  that  is  leaving  the 
cylinder  jackets,  which  is  the  maximum  temperature  of  the 
water  in  the  system. 

LUBRICATION 

Any  internal  combustion  engine  has  a  great  many  sliding 
and  bearing  surfaces.  Friction  is  ever  present  at  these  points 
and  must  be  minimized  for  efficient  operation.  Not  only  does 
friction  cause  loss  of  useful  power,  but  it  also  generates  heat. 
To  minimize  both  these  effects  some  good  lubricant  must  be 
used,  so  that  an  oil  film  may  be  established  between  sliding  and 
bearing  surfaces.  This  metal  to  metal  contact  will  be  avoided 
and  friction  consequently  reduced. 

In  all  naval  aviation  engines  oiling  is  sent  to  the  various 
parts  by  pressure  maintained  by  a  pump  usually  of  the  rotary 
gear  type.  The  oil  being  under  pressure  is  sent  through  tubes 
or  ducts  to  the  various  bearing  points. 

It  may  then  be  seen  that  oiling  troubles  may  be  detected  in 
two  ways,  by  temperature  and  also  by  pressure.  A  gauge  is 
provided  for  recording  both  these.  These  are  the  pulses  of  the 
oiling  system  and  here  again  the  pilot  must  observe  the  tem- 
perature and  pressure  of  the  oil  at  all  times.  Sudden  increases 
or  drops  in  either  should  be  investigated  at  once. 

Oil  may  be  carried  in  the  sump  of  the  engine  or  in  outside 
reservoirs  at  a  level  above  the  oil  pump.  In  the  latter  case 
the  engine  is  said  to  have  a  dry  sump.  This  type  is  advan- 
tageous for  two  reasons.  The  oil  is  well  cooled  by  being  cir- 
culated through  the  outside  reservoir  and  there  is  no  danger 
of  oil  from  the  sump  flooding  the  cylinder  when  the  machine 
is  at  a  heavy  angle.  There  is  a  return  pump  provided  to  take 
oil  from  the  sump  and  return  it  to  the  reservoir. 

24 


In  the  average  pressure  system  oil  is  forced  from  the  pump 
through  a  strainer  to  the  crank  shaft,  camshaft,  pump  and 
magneto  drive  shaft  bearings  direct.  However,  oil  must  be 
conveyed  through  passages  drilled  in  the  crank  shaft  to  the 
crank  pin  bearings  on  account  of  their  rotation.  From  here 
the  cylinder  walls,  piston  pin  bearing,  etc.,  may  be  lubricated 
in  two  ways.  Since  the  big  end  connecting  rod  bearings  must 
have  clearance,  oil  will  be  forced  out  due  to  the  pressure.  This 
will  be  beaten  into  a  fine  mist  by  the  revolving  crank  shaft  and 
thrown  upwards,  lubricating  cylinder  walls,  piston  pin,  etc. 
This  type  of  oiling  is  called  Force  Feed.  In  some  engines  this 
is  not  considered  positive  enough.  Accordingly  a  duct  is  run 
from  the  big  end  connecting  rod  bearing,  along  the  rod,  to  the 
piston  pin.  This  supplements  the  force  feed  system  and  is 
called  a  Full  Force  Feed  system. 

Oil  is  transferred  under  pressure  from  a  stationary  bearing 
to  the  inside  of  a  rotating  shaft  by  a  hole  in  the  shaft  wnich 
registers  once  every  revolution  with  the  supply  lead  to  the 
bearing.  This  method  is  used  to  carry  the  oil  from  the  crank 
shaft  bearing  into  the  hollow  crank  shaft  and  from  the  crank 
pin  to  the  connecting  rod,  and  thence  up  the  connecting  rod 
duct  to  the  piston  pin;  this  latter  being  in  the  full  force  feed 
system.  Only  a  small  portion  of  the  oil  is  actually  consumed, 
the  rest  returns  to  the  sump,  and  thence  to  the  reservoir,  if  the 
sump  is  of  the  dry  type,  and  is  used  over  again. 

Particular  attention  must  be  given  to  the  oil  temperature. 
It  must  be  moderate  so  that  the  oil  may  retain  good  lubricating 
qualities.  Here  again  is  another  advantage  of  the  dry  sump 
since  this  system  also  serves  to  cool  the  oil.  It  is  just  as 
necessary  to  watch  oil  pressure,  which  must  be  maintained 
within  certain  limits  for  efficient  lubrication.  In  most  cases 
there  is  a  Pressure  Relief  Valve  provided  by  which  pressure 
may  be  regulated  or  at  least  limited.  This  consists  simply  of  a 
valve  held  seated  in  some  main  oil  passage  by  a  spring  set  to 
withstand  a  certain  pressure.  This  limits  maximum  pressure, 

25 


which  is  necessary  to  prevent  flooding  of  the  engine  with  too 
much  oil.  The  oil  pressure  meter  must  be  carefully  watched. 
Very  often  serious  accidents  may  be  averted  by  paying  atten- 
tion to  sudden  pressure  drops  which  are  always  an  indication 
of  trouble. 

Oil  loses  its  body  after  being  used,  also  it  collects  fine  par- 
ticles of  metal  from  bearings,  etc.  It  is  therefore  poor  economy 
to  use  oil  too  much.  It  should  be  changed  often.  More  often 
at  first  in  a  new  motor,  since  the  wear  on  bearings  will  be 
greatest  at  first.  When  the  motor  is  torn  down  all  oil  leads 
should  be  carefully  cleaned  out  to  prevent  collection  of  any- 
thing which  would  tend  to  form  obstructions. 

CARBURETION 

Carburetion  is  the  process  of  saturating  air  with  hydro- 
carbon in  the  correct  proportion  for  a  combustible  mixture. 
The  most  important  function  which  a  carburetor  has  to  perform 
is  to  supply  to  the  engine,  under  all  conditions  of  load,  speed 
and  throttle  opening,  a  mixture  of  such  proportions  of  gasoline 
and  air  as  will  result  in  the  most  complete  combustion  and 
maximum  power. 

It  has  been  found  that  the  correct  mixture  should  consist 
of  approximately  fifteen  parts  of  air  to  one  part  of  gasoline 
by  weight. 

The  Zenith  carburetor  is  being  widely  used  for  aviation 
work  because  of  its  simplicity,  as  mixture  compensation  is  se- 
cured by  a  compound  nozzle  arrangement  that  gives  very  good 
results  in  practice.  To  understand  the  carburetor  we  will  have 
to  consider,  first,* the  simple  type  of  carburetor. 

A  simple  carburetor  consists  of  a  single  jet  or  nozzle 
placed  in  the  path  of  incoming  air.  The  gasoline  is  fed  to 
this  jet  or  nozzle  by  a  float  chamber.  It  is  natural  to  suppose 
that  as  the  suction  of  the  engine  increases  the  flow  of  gasoline 
and  air  will  increase  in  the  same  proportion.  This,  however, 

26 


is  not  the  case.  There  is  a  law  of  liquid  bodies  which  states 
that  the  flow  of  gasoline  from  the  jet  increases  under  suction 
faster  than  the  flow  of  air,  giving  a  mixture  which  grows 
richer  and  richer  as  the  engine  speed  increases.  A  mixture 
containing  much  more  gasoline  at  high  speed  than  at  low.  It 
is  easily  seen  from  this  that  the  simple  type  of  carburetor 
would  give  very  unsatisfactory  results  and  could  not  be  used. 
The  common  method  used  to  correct  this  defect  is  to  attach 
auxiliary  air  valves  which  add  air  and  tend  to  dilute  the  mix- 
ture as  it  gets  too  rich.  These  auxiliary  air  valves,  however, 
are  very  hard  to  gauge  and,  having  delicate  springs,  get  out  of 
order  very  easily,  and  are  nothing  more  than  a  makeshift. 

The  Zenith  system  of  compound  nozzle  depends  upon  the 
compensating  effect  of  one  jet  giving  a  leaner  and  leaner  mix- 
ture, as  engine  speeds  increase,  upon  the  jet  of  the  simple  car- 
buretor as  described  above.  To  do  this  the  principle  of  con- 
stant flow  is  used.  Accordingly  a  device  allowing  a  fixed 
amount  of  gasoline  to  flow  by  gravity  into  a  well  wrhich  is  open 
to  the  air,  is  made  use  of.  One  jet  may  then  be  connected 
direct  to  the  float  chamber.  This  is  known  as  the  main  jet  and 
naturally  gives  a  richer  and  richer  mixture  as  engine  speeds 
increase.  Another  jet  may  now  be  placed  around  the  main  jet, 
connecting  with  the  atmospheric  well.  This  is  known  as  the 
Cap  Jet.  The  constant  flow  device  (the  compensator)  then 
delivers  a  steady  rate  of  flow  of  gasoline  per  unit  of  time,  and 
as  the  suction  of  the  motor  increases  more  air  is  drawn  in 
while  the  amount  of  gasoline  remains  the  same  and  the  mix- 
ture grows  poorer  and  poorer.  By  combining  these  two  types 
of  rich  and  poor  mixture  jets  the  Zenith  compound  nozzle  was 
evolved. 

One  jet  counteracts  the  defects  of  the  other,  so  that  from 
the  starting  of  the  engine  to  its  highest  speed  there  is  a  consant 
ratio  of  air  and  gasoline  to  supply  an  efficient  mixture.  In 
addition  to  the  compound  nozzle  the  Zenith  is  equipped  with  an 
idling  device.  When  the  throttle  is  nearly  closed  the  compound 

27 


FIGURE  1 


FIGURE  2 


FIGURE  3 


FIGURE  4 


28 


PRIMING  HOLE  U 


PRIMING  TUBE  J 


BUTTERFLY  T 


SECONDARY 
WELL  P 


CHOKE  X 


CAP  JET  M 


MAIN  JET  O 

Cross  Section  of 
Zenith  Carburetor 


COMPENSATOR  I 


FIGURE  5 
Explanation  of  preceding  figures   1,  2,  3,  4,  5. 

T.     Butterfly  valve   (sometimes  called  throttle  valve). 
Float  chamber. 

Venturi  (sometimes  called  choke). 
Jet.      (In  Zenith  Main  Jet.) 
Main  well. 
Compensator. 
Cap  jet. 

Passage  through  which  gasoline  flows  to  main  jet. 
Passage  through  which  gasoline  flows  to  cap  jet. 
The  arrows  indicate  the  flow  of  air. 

Figure  1  shows  a  simple  type  of  carburetor,  the  jet  G  is  placed 
in  the  path  of  incoming  air,  the  suction  of  the  jet  is  created  by 

29 


F. 
X. 

G. 
J. 

H. 
E. 
K. 


the  Venturi  X,  the  smallest  internal  diameter  of  which  is  located 
at  the  opening  of  the  jet.  It  has  been  explained  that  this  type  of 
carburetor  would  supply  an  increasingly  rich  mixture  as  the  suction 
increased.  The  air  valve  shown  in  figure  2  was  fitted  in  order  to 
admit  air  above  the  jet  and  not  increase  the  suction  on  the  jet. 
This  valve  did  not  prove  a  success  on  aviation  engines,  for  several 
reasons.  The  Zenith  uses  the  compound  nozzle  as  shown  in 
figure  4.  The  main  jet  G  supplies  as  mixture  that  grows  richer 
and  richer  as  the  speed  increases,  and  a  mixture  that  grows  leaner 
and  leaner  as  the  speed  increases. 

The  action  of  the  cap  jet  is  shown  in  figure  3  as  follows: 
The  compensator  I,  feeds  gasoline  into  the  main  well  J,  which 
is  open  to  atmospheric  pressure,  suction  on  the  cap  jet  H,  would 
draw  this  gasoline  out  of  the  main  well  J,  but  owing  to  the  main 
well  being  open  to  atmospheric  pressure,  the  flow  of  gasoline 
through  the  compensator  I,  would  not  increase,  the  suction  on  the 
compensator  being  relieved  by  the  air  held  in  the  top  of  the  main 
well.  The  mixture  supplied  by  the  cap  jet  would  therefore  grow 
leaner  and  leaner  as  the  speed  increased.  This  compound  jet  main- 
tains a  constant  mixture  of  gasoline  and  air  at  all  speeds. 

Figure  5  shows  a  cross  section  of  a  complete  Zenith  carburetor, 
the  butterfly  valve  T,  is  shown  in  the  idling  position,  there  being 
no  suction  on  the  jets,  the  main  well  will  fill  with  gasoline  to  the 
level  of  the  gasoline  in  the  float  chamber.  The  suction  then  comes 
on  the  priming  hole  U,  and  gasoline  will  be  drawn  out  of  the 
main  well,  through  the  priming  tube  J,  this  amount  of  gasoline 
being  regulated  by  the  size  of  the  hole  in  the  secondary  well  P, 
and  the  regulating  screw  O. 


nozzle  gives  no  gasoline,  but  as  there  is  considerable  suction  at 
the  edge  of  the  butterfly  valve,  gasoline  is  drawn  through  a 
small  hole  drilled  in  the  body  of  the  carburetor  and  connected 
to  an  idling  jet  which  is  submerged  in  the  gasoline  that  is  in  the 
well. 

A  carburetor  adjusted  to  supply  a  properly  proportioned 
mixture  at  sea  level  will  supply  in  increasingly  rich  mixture  as 
the  machine  mounts  to  higher  altitudes,  due  to  the  difference  in 
temperature,  density  and  quantity  of  oxygen  in  the  air.  To 
overcome  this  an  altitude  adjustment  is  used.  In  the  ordinary 
Zenith  this  is  simply  a  butterfly  valve  which  may  be  opened  by 

30 


the  pilot  allowing  more  air  to  enter  the  top  of  the  mixing  cham- 
ber, thus  making  up  for  the  loss  in  density  due  to  higher  alti- 
tudes. This  adjustment  does  not  interfere  with  the  suction  at 
the  jets  to  any  extent,  but  simply  admits  more  air. 

The  effect  of  altitude  in  carburetion  is  illustrated  in  the 
following  paragraphs  taken  from  an  article  written  by  the 
Zenith  Carburetor  Company: 

"In  regard  to  the  necessity  of  changing  jets  in  the  Zenith 
Carburetor  in  the  higher  altitudes  above  sea  level,  we  have  no 
hard  and  fast  rule  governing  the  different  sizes  according  to 
variation  in  elevation.  The  Zenith  Carburetor  varies  so  greatly 
from  the  air  valve  carburetor  that  the  effect  of  altitude  is  very 
much  less  with  this  type  of  carburetor,  due  to  the  surface  of 
the  air  valve,  also  the  tension  of  the  spring  being  very  sensi- 
tive to  the  reduced  atmospheric  pressure.  For  instance,  we 
have  at  sea  level  atmospheric  pressure  of  14.7  pounds  per 
square  inch;  at  5,000  ft.,  12.18  pounds;  at  8,000  ft.,  10.87 
pounds;  at  10,000  ft.,  9.96  pounds;  at  12,000  ft.,  9.31  pounds. 

"It  will  be  very  readily  seen,  with  this  great  reduction  in  at- 
mospheric pressure  action  upon  spring  and  valve,  it  would  be 
necessary  to  make  this  spring  very  much  weaker,  whereas  in  the 
Zenith  Carburetor  we  have  no  valves  or  springs  regulating  the 
amount  of  air  taken  in.  Therefore,  very  great  differences  in 
altitude  have  very  little  effect  on  the  actual  operation  of  the 
Zenith  Carburetor. 

"Just  a  little  data  on  the  effects  of  altitude  in  regard  to  the 
gasoline  motor  developing  its  rated  horse-power. 

"Air  consists  of  two  gases — oxygen  and  nitrogen — in  the 
proportion  of  l/5th  oxygen  and  4/5th  nitrogen  by  weight. 
This  proportion  holds  good  all  through  the  atmosphere  from 
the  bottom  to  the  top.  Oxygen  is  the  element  that  supports 
combustion.  Consequently,  if  we  go  to  a  higher  altitude,  where 
the  air  pressure  is  less,  a  given  volume  of  air  will  not  weigh 
as  much  as  a  similar  volume  at  sea  level.  It  will  not  contain 
as  much  oxygen. 

31 


"From  this  we  see  that  a  cylinder  full  of  air  at  sea  level 
will  contain  a  greater  weight  of  oxygen  than  the  same  cylinder 
on  the  top  of  a  high  mountain. 

"Assuming  the  carburetor  adjustment  to  be  the  best  for 
efficient  running  at  sea  level,  with  altitude  valve  closed,  it  will 
be  advisable  to  start  opening  the  altitude  valve  at  about  2,500 
feet  elevation  and  keeping  it  as  far  open  as  possible  without 
reducing  the  engine  r.  p.  m. 

"Extensive  test  have  shown  that — above  5,000  feet  eleva- 
tion— change  in  engine  power  will  be  negligible,  but  that  con- 
sumption of  fuel  will  be  reduced  from  8  per  cent,  to  10  per  cent, 
by  operating  the  engine  with  the  altitude  valve  open." 

There  is  another  general  type  of  carburetor  coming  more 
and  more  into  prominence  known  as  the  multiple  jet  type. 
Under  this  heading  come  the  Miller  and  the  Master.  A  num- 
ber of  jets  are  set  in  a  straight  line,  and  so  arranged  that  the 
size  of  the  jets  increase  progressively.  The  throttle  valve  is 
of  the  barrel  type,  which  more  nearly  approximates  the  action 
of  a  variable  venturi.  On  opening  the  throttle  to  speed  up,  the 
jets  are  uncovered  progressively.  In  this  way  a  very  strong 
venturi  action  is  centered  at  slow  speeds  over  one  or  two 
small  jets  and  as  the  speed  is  increased  this  action  is  decreased. 
The  additional  gas  being  provided  by  the  remaining  jets  as 
suction  reaches  them.  Carburetors  of  this  type  are  simple  in 
construction  and  easily  maintained  once  they  are  regulated. 
This  can  be  done  only  by  a  careful  study  of  the  engine  demands 
and  adaptation  of  suitable  jets  in  accordance.  One  regulated 
they  are  singularly  free  from  adjustments. 

The  Stromberg  Company  has  recently  developed  a  car- 
buretor for  aviation  purposes  which,  on  recent  tests,  has  given 
excellent  results. 

The  Stromberg  carburetor  maintains  the  proper  mixture 
by  what  is  known  as  an  air-bled  jet.  Gasoline  leaves  the  float 
chamber,  passes  the  point  of  a  high-speed  adjustment  needle, 
and  enters  a  vertical  channel  or  well.  Air  is  taken  into  this 

32 


channel  through  the  air-bleeder,  or  air  adjustment.  This  air 
discharges  into  the  gasoline  channel  through  small  holes  and 
beats  up  the  gasoline  into  a  fine  spray.  This  then  enters 
through  a  number  of  jets  into  the  high  velocity  air  stream  of 
a  small  venturi.  There  is  a  second  or  large  venturi  provided 
through  which  the  mixture  next  passes.  Since  good  excellera- 
tion  requires  a  temporary  enrichment,  there  is  a  reserve  cham- 
ber or  excellerating  well  provided  which  is  concentric  to  and 
communicates  with  the  vertical  channel  mentioned  above. 
With  the  motor  idling  or  slowing  down,  this  well  fills  with 
gasoline  and  whenever  the  venturi  suction  is  increased  by  open- 
ing the  throttle,  the  level  in  the  well  goes  down  and  the  gaso- 
line thus  displaced  adds  to  the  amount  entering  the  small 
venturi. 

The  carburetor  is  also  provided  with  an  idling  device.  In 
the  center  of  the  vertical  channel,  there  is  located  a  long  tube 
which  extends  up  the  side  of  the  carburetor,  and  has  an  en- 
trance to  the  mixing  chamber  through  a  small  hole  at  the  level 
of  the  butterfly  valve;  when  the  throttle  is  closed,  or  nearly 
closed,  gasoline  enters  through  this  small  hole.  The  proper 
mixture  is  maintained  by  regulating  the  admission  of  air  into 
the  idling  tube  by  an  idling  adjustment  screw.  This  idling  ad- 
justment does  not  work  after  the  throttle  has  been  opened,  so 
that  the  engine  runs  above  idling  speed. 

There  is  still  another  type  of  carburetor  which  furnishes 
the  proper  mixture  at  all  speeds  by  means  of  a  variable  ven- 
turi. Many  models  have  been  constructed  using  this  idea  but 
they  are  to  the  greatest  extent  still  in  experimental  stages  and 
so  far  are  a  great  ways  from  perfection.  The  adoption  of 
this  principle  would  be  ideal  and  there  are  several  corburetors 
which  attempt  to  approximate  it  in  various  ways. 

EFFECTS  OF  IMPROPER  CARBURETION 

As  already  stated  the  problem  of  carburetion  is  to  main- 
tain the  proper  mixture  at  all  engine  speeds.  There  are  numer- 

33 


ous  effects  which  will  give  indications  of  an  improper  mixture. 
First  let  us  consider  the  effects  of  a  lean  mixture;  that  is,  a 
mixture  in  which  there  is  too  little  gasoline  per  unit  of  air. 

The  lean  mixture  will,  in  the  majority  of  cases,  be  made 
evident  by  back-firing  or  spitting  back  of  the  carburetor.  The 
cause  of  this  is  that  the  mixture,  containing  too  little  volatile 
matter,  will  be  slow  burning,  and  some  of  it  will  still  be  burn- 
ing when  the  intake  valve  opens  on  the  next  succeeding  stroke. 
Naturally  this  will  cause  ignition  of  the  gases  in  the  intake 
manifold  and  a  back-fire  will  result.  This  is  very  dangerous 
as  fire  is  likely  to  result  if  the  carburetor  is  not  placed  where 
it  will  be  away  from  any  gasoline  drip  which  may  have  col- 
lected. A  lean  mixture  being  slow  burning  will  expose  more 
cylinder  wall  to  heat  than  a  proper  mixture,  and,  therefore,  it  is 
said  that  overheating  will  result.  There  will  be  a  tendency 
toward  this,  but  it  is  generally  conceded  that  this  effect  is 
neutralized  to  a  great  extent  by  the  cooling  effect  of  the  addi- 
tional air  present  in  the  mixture.  Naturally  an  engine  running 
on  too  lean  a  mixture  will  not  develop  the  proper  power. 

A  rich  mixture  is  also  slow  burning.  It,  however,  does 
not  cause  a  back-fire  but  will  cause  an  after-fire.  It  is  naturally 
a  heavier,  more  homogeneous  gas  than  a  lean  mixture  and 
consequently  none  of  it  is  left  in  the  cylinder  after  the  exhaust 
stroke.  Therefore,  back-fire  cannot  occur,  but  a  loud  exhaust 
or  after-fire  will  result. 

Also,  on  account  of  slow  burning,  overheating  will  result, 
since  more  cylinder  wall  than  should  be  is  exposed  to  the  burn- 
ing gases  and  the  cooling  system  will  be  over-taxed.  Due  to  the 
greater  amount  of  carbon  present  in  the  mixture,  and  its  in- 
complete combustion,  the  formation  of  carbon  will  proceed 
more  rapidly  with  its  consequent  detrimental  results.  A  rich 
mixture  will  also  result  in  loss  of  power. 

An  expert  can  tell  by  the  color  of  the  exhaust  flame  the 
exact  condition  of  the  carburetion  system.  The  proper  flame 
is  almost-  an  invisible  blue,  while  a  yellowish  flame  indicates  a 

34 


lean  mixture  and  a  red  flame,  accompanied  in  bad  cases  by 
black  smoke,  a  rich  mixture. 

ELECTRICITY  AND  MAGNETISM 

Units : 

Volt  =  Unit  of  pressure. 

Amperes  =  Rate  of  flow. 

Ohm          ==  Unit  of  resistance. 

Watt          =  Unit  of  power  (Volts  X  amperes). 

Resistance  is  the  opposition  that  any  material  offers  to 
the  flow  of  an  electric  current. 

A  conductor  is  a  metallic  substance  of  low  resistance  that 
is  used  to  conduct  an  electric  current;  viz:  a  coil  of  copper 
wire. 

An  insulator  (non-conductor)  dielectric  any  substance  of 
such  high  resistance  that  practically  no  current  can  flow  through 
it.  (Glass,  porcelain,  rubber,  etc.) 

Magnetism  is  the  invisible  field  of  forces  operating  be- 
tween the  poles  of  a  magnet,  and  in  circular  rings  about  a 
wire  through  which  a  current  is  flowing.  This  magnetic  field 
exists  in  the  form  of  lines  of  force,  or  flux.  The  permanent 
magnet  is  usually  made  in  the  form  of  a  horse  shoe,  and  is 
always  used  to  furnish  the  magnetic  field  in  a  magneto.  In  a 
generator  and  in  the  battery  type  ignition,  an  electro  magnet 
is  used.  This  is  not  a  permanent  magnet,  and  only  sets  up 
a  magnetic  field  as  long  as  electricity  is  flowing  through  the 
conductor  that  is  wound  around  its  soft  iron  core. 

INDUCTION 

Induction  may  be  taken  to  mean,  in  simple  words  and 
for  present  purposes,  causing  an  electric  current  to  exist.  This 
may  be  accomplished  in  three  ways : 

1.  Passing  a  conductor  through  a  magnetic  field  or  lines  of 

35 


force,  thereby  causing  the  conductor  to  cut  the  field  and  in- 
ducing a  voltage  in  it  and  current,  if  a  closed  circuit.  That 
is,  having  a  stationery  field  and  a  moving  conductor. 

2.  Reversing  the  above  condition,  that  is,  having  a  station- 
ary conductor,  but  a  movable  field. 

3.  Having  both  conductor  and  field  stationary  and  induc- 
ing  a   current   by   changing   field   strength,   that   is,   causing  a 
change   in   the  value   of  the   flux. 

IGNITION 

After  the  gas  has  been  compressed  by  the  compression 
stroke,  it  must  be  ignited  in  order  to  furnish  the  expansion 
necessary  to  force  the  pistom  down  for  the  power  stroke.  A 
spark  plug  consisting  of  two  electrodes,  separated  by  an  in- 
sulating material,  is  screwed  into  the  combustion  chamber  of 
the  cylinder.  The  two  electrodes  are  separated  at  their  ends 
or  points  by  an  air  gap,  and  by  causing  an  electric  spark 
to  jump  this  gap,  the  compressed  gas  is  ignited.  The  electric 
current  necessary  to  jump  across  the  spark  plug  gap  is  fur- 
nished by  the  ignition  system,  which  can  be  of  the  magneto 
or  battery  type. 

The  ordinary  current  furnished  by  a  battery  or  generator 
is  not  of  sufficient  voltage  or  pressure  to  jump  across  the  gap 
of  the  spark  plug,  and  in  order  to  raise  the  voltage  of  the 
battery  or  generator,  an  induction  coil  is  incorporated  in  the 
ignition  system,  and  supplies  the  high  voltage  current  nec- 
essary to  jump  the  spark  plug  gap. 

If  a  conductor  is  coiled  about  a  soft  iron  core,  and  cur- 
rent is  caused  to  flow  through  the  coil,  the  core  will  become 
a  magnet,  thereby  causing  a  magnetic  field  to  be  established. 
The  moment  current  ceases  to  flow  in  the  coil  the  core  ceases 
to  be  a  magnet  and  consequently  its  magnetic  field  collapses. 
Now,  if  a  second  coil  be  wrapped  about  this  first,  the  collapse 
of  the  magnetic  field,  caused  by  breaking  the  circuit  of  the 

36 


first  coil,  will  induce  a  current  in  the  second.  This  is  the 
principal  of  the  induction  coil.  The  first  coil  which  causes 
the  core  to  be  magnetized  and  de-magnetized,  is  called  in  the 
primary.  The  second  or  out  coil  is  the  secondary.  Both  are 
wound  on  the  core,  the  secondary  over  the  primary. 

The  primary  coil  consists  of  a  comparatively  small  num- 
ber of  turns  of  coarse  wire  while  the  secondary  contains  a 
large  number  of  turns  of  very  fine  wire.  The  desired  result 
is  to  obtain  high  voltage  or  high  pressure  which  will  be  capa- 
ble of  breaking  down  the  resistance  of  the  spark  plug  gap. 
Consequently,  the  induced  or  secondary  current  must  be  of  high 
voltage  or  high  tension.  As  it  is  impossible  to  get  something 
from  nothing  the  power  or  \vattage  of  both  primary  and  secon- 
dary circuits  must  be  theoretically  the  same.  Consequently,  the 
secondary  must  be  of  low  current  value  in  order  to  allow  the 
higher  voltage  value  since  wattage  must  remain  constant. 

It  can  then  be  understood  why  fine  wire  is  used  for  sec- 
ondary purposes.  Simply  because  it  will  not  be  conductive 
to  heavy  amperage;  in  fact  will  make  it  impossible  for  heavy 
amperage  to  exist  and  the  result,  since  wattage  must  be  the 
same  as  in  the  primary,  will  be  high  voltage  value. 

Since  the  induced  voltage  is  directly  proportional  to  the 
ratio  of  the  number  of  turns  in  the  secondary  coil  to  the 
number  of  turns  in  the  primary,  it  may  be  easily  seen  why 
the  secondary  will  consist  of  a  large  number  of  turns;  bear- 
ing in  mind  that  the  desired  result  is  high  voltage. 

Breaker  Mechanism: 

The  intensity  of  induced  voltage  will  also  be  greatly  de- 
pendent upon  the  rapidity  with  which  the  secondary  coil  is 
cut  by  the  collapsing  field.  That  is,  maximum  voltage  will  be 
dependent  upon  maximum  rate  of  change  of  flux.  The  most 
effective  method  of  obtaining  this  result  is  to  suddenly  in- 
terrupt the  flow  of  primary  current,  thus  stopping  the  genera- 
tion of  lines  of  force  by  it,  and  changing  instantaneously 

37 


the  number  of  lines  of  force  through  the  secondary  from  a 
maximum  to  zero.  The  device  which  interrupts  the  primary 
circuit  is  the  Breaker  Mechanism,  consisting  of  two  breaker 
points,  one  stationary — the  other  held  in  contact  by  a  lever 
and  spring.  The  cam  acts  on  the  lever  causing  these  points 
to  separate  and  break  the  primary  circuit. 

Condenser : 

Current  is  flowing  around  the  primary  circuit  at  the 
moment  of  interruption  by  the  breaker  points,  and  due  to  its 
own  inertia,  it  tends  to  keep  on  flowing  and  jump  across  the 
air  gap  created  by  the  separation  of  the  breaker  points.  If 
no  provision  were  made  to  stop  this  condition,  the  induced 
or  secondary  voltage  would  not  be  as  intense  as  possible.  The 
reason  for  this  would  be  that  due  to  the  leakage  across  the 
points  the  collapse  of  the  magnetic  field  would  not  be  abrupt. 
It  has  been  pointed  out  that  the  more  rapid  the  collapse,  the 
more  intense  the  ^induced  voltage ;  hence  this  leakage  must  be 
stopped.  Not  only  will  the  induced  voltage  be  poor,  but  the 
breaker  points  will  become  badly  pitted  due  to  the  arcing 
across  the  air  gap  created.  This  would  make  it  impossible 
to  keep  the  points  clean,  well  surfaced  and  at  correct  adjust- 
ment, all  of  which  would  be  decidedly  detrimental.  To  over- 
come these  defects  a  condenser  is  connected  around  the  breaker 
points.  A  condenser  is  composed  of  alternate  layers  of  a  con- 
ductor and  a  dielectric,  very  often  tin  foil  being  used  for  the 
former  and  mica  for  the  latter. 

The  alternate  layers  of  the  conductor  are  connected  to 
opposite  terminals  of  the  device.  Hence  there  is  no  path  for 
current  through  the  condenser,  but  it  acts  as  a  reservoir.  When 
the  breaker  points  separate,  the  current  flows  into  the  con- 
denser instead  of  arcing  across  the  points.  When  the  con- 
denser is  fully  charged  it  rapidly  discharges  in  the  reverse 
direction,  thereby  causing  a  sudden  reversal  of  magnetic  flux, 
and  this  condition  continues,  producing  an  oscillatory  current 

38 


of  very  high  frequency  until  the  current  value  becomes  so 
reduced  that  the  action  must  cease.  This  oscillatory  discharge 
has  its  effect  on  the  secondary  induction,  the  result  being  a 
prolonged  spark  assisting  in  overcoming  the  resistance  of  the 
spark  plug  gap  and  insuring  better  ignition.  At  times  some 
of  the  dielectric  substance  will  be  punctured  thus  reducing  the 
capacity  of  the  condenser  and  making  it  necessary  for  part  of 
the  current  to  jump  across  the  breaker  points.  Where  pitted 
points  are  found  the  operator  can  be  practically  positive  that 
the  condenser  is  faulty.  If,  however,  the  condenser  becomes 
entirely  burned  out,  the  result  will  be  a  short  circuiting  of 
the  breaker  points  and  no  interruption  of  the  primary,  result- 
ing in  no  ignition. 

Breaker  Point  Adjustment: 

In  every  ignition  system  there  is  a  certain  maximum 
distance  of  opening  for  which  the  breaker  points  are  designed. 
They  must  be  kept  in  adjustment  so  that  the  opening  will  al- 
ways be  correct.  Suppose  the  opening  prescribed  is  to  be 
0.020"  and  the  adjustment  is  faulty  so  that  the  opening  per- 
mitted is  above  the  net  amount.  Naturally  it  will  take  longer 
for  the  points  to  return  to  contact.  This  will  result  in  a 
considerable  lag  at  high  engine  speeds,  and  it  is  common  to 
have  this  condition  drag  out  to  such  an  extent  that  ignition 
will  fail  for  as  much  as  one  complete  revolution.  The  re- 
sult, then,  of  too  great  a  gap,  will  be  faulty  ignition  and  con- 
sequently misfiring.  If  the  opening  is  below  the  prescribed 
amount,  the  resistance  of  the  air  gap  will  reach  a  point  where 
it  will  be  below  the  resistance  of  the  primary  coil.  Then 
when  the  condenser  discharges,  instead  of  going  through  the 
coil,  the  current  will  arc  across  the  points,  the  result  being 
the  same  as  given  by  a  faulty  condenser.  Again  the  result 
will  be  faulty  ignition. 

It  may  then  be  seen  that  correct  breaker  point  adjustment 
is  imperative  for  proper  engine  running. 

39 


Distributor : 

The  spark  will  jump  across  the  spark  plug  gap  when 
the  current  induced  in  the  secondary  is  at  a  maximum  value, 
in  other  words,  when  the  breaker  mechanism  interrupts  the 
primary  current.  Hence,  the  breaker  mechanism  must  be 
timed  to  the  engine  so  that  the  spark  will  occur  at  the  proper 
time.  If  only  one  cylinder  is  to  be  ignited,  the  secondary 
wire  can  be  led  directly  to  the  spark  plug.  However,  when 
more  than  one  cylinder  is  used,  a  device  must  be  introduced 
to  direct  the  high  tension  secondary  current  to  the  proper 
cylinder.  This  device  is  called  a  distributor,  and  consists  of 
a  rotating  arm  which  touches  one  contact  for  each  cylinder 
in  succession.  A  wire  leads  from  each  contact  to  its  cylinder. 
Hence,  when  the  primary  circuit  is  broken,  a  spark  will  be 
flashed  in  the  cylinder  with  whose  segment  the  distributor  arm 
is  making  contact. 

Ground : 

In  order  to  simplify  wiring,  one  end  of  both  the  primary 
and  secondary  circuits  is  attached  to  some  metal  part  of  the 
engine.  Thus  the  metal  of  the  engine  serves  as  one  wire  of 
the  circuit,  and  is  known  as  the  "ground." 

Primary  Circuit: 

The  primary  circuit  consists  of  a  source  of  current,  for 
example,  a  storage  battery,  with  one  terminal  wired  to  the 
ground,  the  other  terminal  leads  the  current  to  the  primary 
windings  of  the  induction  coil;  from  the  coil  the  current  goes 
through  the  breaker  mechanism  and  then  to  the  ground;  the 
condenser  is  connected  around  the  breaker  mechanism. 

Secondary  Circuit: 

One  end  of  the  secondary  coil  is  attached  to  the  ground; 
the  other  ends  conducts  the  high  tension  current  to  the  dis- 
tributor arm;  from  there  it  goes  to  the  spark  plug  as  deter- 

40 


mined  by  the  proper  distributor  segment  jumps  across  the  gap, 
to  the  ground. 

MAGNETOS 

A  magneto  contains  all  the  elements  of  the  ignition  system 
previously  described,  and  has  the  same  primary  and  secondary 
circuits.  It  differs,  however,  in  that  it  generates  its  own 
primary  current,  again  by  the  principle  of  induction.  There  are 
two  main  methods  of  doing  this.  In  both  cases  lines  of  force  are 
furnished  by  permanent  magnets.  The  first  type  of  magneto 
to  be  discussed  is  that  in  which  the  charge  in  the  number  of 
lines  of  forms  through  the  coils  is  accomplished  by  rotating 
the  coils  in  the  magnetic  field  created  by  the  permanent 
magnets.  The  intensity  of  the  primary  current  induced  in  this 
case  depends  to  a  great  extent  on  the  rate  of  change  of  flux, 
which  varies  with  the  speed  of  rotation  of  the  coils.  The 
coils  are  wound  on  a  rotating  member  called  the  armature, 
and  the  momentary  intensity  of  the  current  depends  on  the  posi- 
tion of  the  armature,  relative  to  the  permanent  magnets. 

The  armature  used  is  of  the  shuttle  type,  a  section  of  it 
being  roughly  that  of  the  capital  letter  I.  The  vertical  part 
of  the  shuttel  then  may  also  perform  the  function  of  a  core 
and  the  coils  are  wound  about  it,  the  primary  first,  then  the 
secondary.  Magnetic  lines  of  force  follow  the  path  of  least 
resistance,  and  it  is  obvious  that  there  will  be  two  points  per 
revolution  of  the  shuttle  where  the  lines  of  force  passing- 
through  the  core  will  change  in  direction.  During  the  reversal 
of  flux,  there  will  be  a  point  if  highest  primary  induction, 
which,  if  utilized  by  opening  the  breaker  points,  will  cause 
maximum  secondary  induction.  It  may  be  seen  that  with  this 
type  of  magneto  it  is  possible  to  obtain  two  sparks  per  revo- 
lution of  the  shuttle. 

Magnetos  of  this  character  are  classified  as  revolving 
shuttle  type,  and  among  them  are  the  Bosch  and  Berling. 

41 


DIXIE  MAGNETO 

The  Dixie  magneto  operates  on  a  principle  entirely  dif- 
ferent from  the  rotating  shuttle  type.  The  magnets  and  wind- 
ings in  the  Dixie  are  both  stationary,  and  the  only  rotating 
member  is  the  rotary  pole  structure. 

The  rotary  pole  structure  is  an  extension  of  the  per- 
manent magnets,  and  it  rotates  across  the  face  of  the  field 
pole  structure.  The  primary  and  secondary  coils  are  wound 
around  a  core  which  is  mounted  on  top  of  the  field  pole 
structure  in  such  a  manner  as  to  form  a  path  for  the  magnetic 
flux  as  it  flows  from  the  rotary  poles.  The  rotary  pole  structure 
having  two  extensions  of  the  north,  and  two  of  the  south, 
arranged  alternately,  gives  four  reversals  of  flux  through  the 
core  of  the  windings  every  revolution  of  the  rotary  pole 
structure.  Consequently,  there  would  be  four  inductions  per 
revolution,  and  one  spark  per  induction.  This  is  a  decided 
advantage  over  the  rotary  shuttle  type  which  gives  two  sparks 
per  revolution,  and  has  to  rotate  twice  as  fast  to  do  the 
same  work. 

From  the  above,  it  can  be  seen  that  the  breaker  mechan- 
ism would  have  to  open  and  close  the  primary  circuit  four 
times  per  revolution;  and  the  Dixie  would  be  timed  to  rotate 
one-half  the  speed  of  a  Bosch  or  Berling  on  the  same  engine. 

Referring  to  the  drawing  on  page  43,  it  can  be  seen  in 
figure  1,  that  the  rotary  pole  structure  A,  is  in  the  position 
of  maximum  flux  flow,  and  that  the  magnetic  flux  is  flowing 
from  the  north  rotating  pole  through  the  field  pole  structure 
C,  thence  through  the  field  pole  D,  and  back  into  the  south 
rotating  pole.  It  can  be  seen  that  a  quarter  revolution  of 
the  rotary  pole  structure  A,  will  give  a  complete  reversal  of  the 
magnetic  flux,  because  the  polarity  would  change  from  south 
to  north  on  one  side  and  north  to  south  on  the  other  side. 
Figure  No.  2  shows  a  complete  reversal  of  flux  flow  which 
was  brought  about  by  a  quarter  revolution  of  the  rotary  pole 

42 


DIXIE-    MA6NE.TO 


KEY- 


A-  ROTARY     POLE     STRUCTURE  1  - 

D-  fiE.1.0    CORE  I- 

E_pRlMfl«Y.    wviNOiNGS  V* 

F-SECOMOARY          -  N 

6  -  CONDENSER 

H-BRERKER    MCCHflNiSM  F,62. 


LEVER 
K-CONTflCTS 

l_-SWrTCM 


43 


structure  A.  As  it  is  this  sudden  reversal  of  flux  that  causes 
the  induction  of  current  in  the  winding,  and  gives  the  spark. 
Four  of  these  reversals  coming  every  revolution  of  the  rotary 
pole  structure,  will  give  off  four  sparks.  It  has  been  ex- 
plained, in  preceding  chapters,  that  the  primary  circuit  must 
be  interrupted  for  every  reversal  of  flux  or  induction,  and  in 
the  Dixie  magneto,  this  is  provided  for  by  a  cam  having  four 
lobes,  and  rotating  at  the  same  speed  as  the  rotary  pole  struc- 
ture. The  windings,  condenser,  breaker  mechanism,  distrib- 
utor, etc.,  are  clearly  shown  in  the  drawing,  a  study  of  which 
will  enable  the  reader  to  clearly  understand  the  Dixie  principle. 

TIMING 

Valve  Timing:  It  has  been  pointed  out  that  there  must 
be  certain  valve  action  during  certain  piston  strokes,  and  that 
the  valve  action  is  controlled  by  the  cam  shaft  which  neces- 
sarily must  turn  at  half  crank  shaft  speed.  It  is  further  neces- 
sary to  conform  to  the  manufacturers'  standards  for  exact 
points  of  valve  opening  and  closing.  The  average  engine  used 
in  naval  aviation  will  conform  within  very  close  limits  to  the 
following  valve  timing: 

Intake  Valve  open    TDC   15°  Past        TDC 

Intake  Valve  closed    35°      past       BDC  50°  Past        BDC 

Exhaust  Valve  open    50°      before  BDC  35°  Before    BDC 

Exhaust  Valve  closed   ....TDC   15°  Past       TDC 

From  this  it  will  be  seen  that  the  following  may  be  assumed 
a  good  average  chart  for  valve  operation : 

Intake  open 10°   Past  TDC 

Intake  close    45°  Past  BDC 

Exhaust  open    50°  Before  BDC 

Exhaust  close    10°  Past  TDC 

This  may  then  be  used  for  the  ensuing  discussion.  It  will 
be  noted  that  valves  very  seldom  open  or  close  on  dead  centers. 
The  distance  by  which  a  valve  opens  or  closes  before  or  after  a 

44 


dead  center  is  usually  measured  as  given,  in  degrees  of  crank 
shaft  rotation.  It  may  also  be  measured,  and  is  occasionally, 
in  linear  distance  of  piston  travel. 

The  intake  valve  is  allowed  to  remain  open  after  the  piston 
has  passed  bottom  center,  in  order  that  a  maximum  charge  of 
gas  may  be  drawn  into  the  cylinder.  The  piston  moving  down 
in  the  cylinder  displaces  space  faster  than  the  restricted  area  of 
the  intake  port  can  allow  it  to  be  relieved,  and  even  though 
the  piston  has  passed  bottom  center,  there  is  still  some  vacuum 
in  the  cylinder,  and  this  vacuum  will  continue  to  draw  in  gas 
as  long  as  it  exists  and  the  intake  valve  is  kept  open  until  this 
vacuum  is  completely  relieved. 

From  the  closing  of  the  intake  to  the  opening  of  the  ex- 
haust there  can  be  no  valve  action,  since  compression  and  power 
must  take  place  and  both  valves  must  be  kept  closed  during 
compression  and  power.  The  exhaust  valve  opens  early,  or 
before  BDC,  primarily  to  insure  complete  scavenging.  At  50° 
before  BDC  the  angularity  of  the  connecting  rod  is  so  small 
that  any  additional  work  given  by  expanding  gases  would  be 
slight.  It  is  then  better  to  utilize  the  expansion  left  in  the 
gases  at  this  part  of  the  stroke  to  aid  scavenging,  thereby  insur- 
ing its  being  more  complete  and  relieving  the  piston  of  part  of 
the  work  on  the  exhaust  stroke.  The  exhaust  valve  is  allowed 
to  remain  open  until  after  TDC  simply  again  to  insure  com- 
plete scavenging. 

The  intake  valve  opens  at  a  point  which  will  allow  equaliza- 
tion of  pressure  in  the  cylinder. 

It  will  then  be  seen  that  it  is  absolutely  necessary  to  time 
the  valves  so  that  their  openings  and  closings  will  be  exactly 
in  accordance  with  the  manufacturers'  specifications,  since 
these  are  given  for  best  engine  running  results. 

In  order  to  time  the  cam  shaft,  and  thereby  the  valves  on 
an  engine  having  one  cam  shaft  on  which  both  exhaust  and 

45 


intake  cams  are  placed,  it  is  necessary  to  accomplish  the   fol- 
lowing things : 

(1)  Determine    the   proper   direction    of   rotation    of   the 
engine. 

This  is  best  done  by  determining  rotation  to  procure  open- 
ing of  the  intake  at  about  the  point  of  exhaust  closing.  It 
may  also  be  accomplished  by  determining  the  proper  direction 
of  rotation  of  water  pump  or  propeller.  In  these  cases  it  is 
necessary  to  take  gear  drives  into  consideration. 

(2)  Adjust  the  Valve  clearance. 

This  must  be  done  when  the  cam  follower  is  on  the  low 
part  or  heel  of  the  cam  so  that  the  valves  will  be  finally  seated. 
Such  a  condition  will  be  sure  to  exist  at  about  TDC  of  com- 
pression stroke.  This  position  may  be  approximated  by  turn- 
ing the  engine  in  correct  direction  to  the  point  of  closing  of  the 
intake  valve,  then  turning  approximately  half  a  revolution 
more. 

(3)  Intake  valve  of  No.  1  cylinder  just  opening. 

This  will  bring  the  cam  shaft  into  its  proper  position  or 
timing. 

(4)  Disconnect  cam  shaft  from  crank  shaft. 

Since  the  cam  shaft  is  in  its  proper  position  it  must  not  be 
moved  further. 

(5)  Place  piston  of  No.   1   cylinder  on  Top  Dead  Center 
and  number  of  degrees  after  TDC  as  specified  by  tlic 
manufacturer  of  intake  valve   to   open. 

This  will  bring  piston  to  point  for  intake  valve  opening. 

(6)  Connect  cam  shaft  to  crank  shaft. 

(7)  Check  Timing  very  carefully. 

For  quick  work  very  often  the  valve  clearance  is  adjusted 
for  timing  purposes  on  No.  1  cylinder  only.  If  this  method  is 

46 


employed,  the  clearance  on  the  remaining  valves  must  be  set 
and  checked  after  timing. 

It  may  then  be  seen  that  valve  timing  consists  merely  of 
making  an  intake  valve  function  when  the  piston  is  at  the 
proper  position  for  such  functioning  to  occur.  Timing  may  be 
done  on  either  opening  or  closing  of  either  valve,  but  it  is 
common  pactice  to  use  intake  opening. 

If  there  is  only  one  cam  shaft  it  is  necessary  to  time  on 
one  valve  only.  If  there  are  more  than  one  cam  shaft,  it  is 
necessary  to  time  each  cam  shaft  separately. 

The  angular  travel  of  the  crank  shaft  may  be  found  by 
means  of  a  timing  disk  which  is  fastened  to  the  crank  shaft. 
This  is  simply  a  disk  graduated  in  degrees. 

If,  as  may  possibly  be  the  case,  the  ignition  system  is 
properly  timed  to  an  engine  during  valve  timing,  it  is  necessary 
to  be  careful  of  the  Top  Dead  Center  used.  Obviously,  spark 
must  occur  at  or  near  TDC  of  compression,  when  both  valves 
must  be  tight  closed. 
Spark  Advance  and  Retard: 

In  order  to  obtain  maximum  power,  combustion  should  be 
complete  and,  therefore,  maximum  pressure  generated,  at  top 
dead  center.  As  a  definite  time  elapses  between  the  flashing 
of  the  spark  and  the  completion  of  combustion,  the  spark  must 
occur  before  top  dead  center,  and  the  faster  the  engines  run 
the  further  in  advance  of  dead  center  it  must  occur.  If  com- 
bustion, due  to  a  late  spark,  were  completed  after  top  dead 
center,  all  power  would  not  be  extracted  from  the  gases  when 
the  exhaust  valve  opens,  and  overheating  would  result.  If  the 
engine  is  turning  over  slowly,  the  spark  must  be  retarded,  or, 
in  other  words,  must  occur  later  in  the  cycle,  or  the  point  of 
maximum  pressure  will  occur  before  top  dead  center,  and  the 
crankshaft  will  receive  an  impulse  to  turn  in  the  wrong  direc- 
tion, giving  rise  to  a  knock.  If  this  occurred  while,  cranking 
the  engine,  it  would  cause  a  back-kick.  Hence  the  spark  must 
be  retarded  when  cranking.  This  variation  in  the  time  of  oc- 

47 


currence  of  the  spark  is  obtained  by  causing  the  cam  to  open 
the  circuit  breaker  points  earlier  or  later. 

This  is  accomplished  by  moving-  the  advance  retard  lever 
in  the  same  direction  as  the  rotation  of  the  magneto  shaft  to 
obtain  retarded  spark  and  in  the  opposite  direction  to  rotation 
to  obtain  advanced  spark. 

Magneto  Timing : 

Since  there  are  two  positions  in  which  the  magneto  may 
be  set,  viz.,  advanced  and  retarded,  it  may  readily  be  seen  that 
there  may  be  two  methods  of  timing,  Advanced  or  Retarded. 

Advanced  Position: 

(1)  Determine  direction  of  rotation  of  engine.     As  given 

under  valve  timing. 

(2)  Determine  direction  of  rotation  of  magneto.     Usually 

indicated  by  an  arrow-  stamped  on  the  oil  cup  at 
the  driving  end. 

(3)  Place  piston  of  No.  1   cylinder  at  top  dead  center  of 

compression  stroke  and  number  of  degrees  before 
TDC  as  specified  by  the  manufacturer  for  ad- 
vanced spark  to  occur.  This  is  usually  from  20° 
to  30°.  This  puts  the  piston  in  position  for  spark- 
to  occur. 

(4)  Fully  advance  the  magneto. 

(5)  Turn  distributor  brush  to  No.  1  segment. 

(6)  Turn  magneto   shaft  until  points  are  just   breaking. 

This  places  magneto  in  position  ready  to  give 
spark. 

(7)  Connect  magneto   to  engine. 

(8)  Find  firing  order  of  engine — by  watching  any  succes- 

sive valve  operation. 

(9)  Connect  distributor  segments  in  accordance  with  firing 

order. 
(10)   Check  up  timing. 

48 


Retarded  position: 

The  same  as  advanced  method,  except  for  the  following: 
In  No.  3  place  piston  of  No.  1  cylinder  at  TDC  of  compression 
stroke.  It  is  always  safe  to  assume  retarded  spark  as  occurring 
here.  If  the  manufacturer  specifies  differently  follow  specifica- 
tions. Some  engines  have  retarded  spark  occurring  a  few 
degrees  after  TDC.  In  No.  4  fully  retard  the  magneto,  other- 
wise follow-  the  advanced  method.  The  advanced  method 
should  be  used  whenever  possible.  Only  use  the  retarded 
method  when  there  is  not  sufficient  data  to  enable  the  use  of 
the  advanced  method. 

Note. — Where  two  or  more  magnetos  are  used  they  must 
be  timed  separately  and  so  as  to  break  at  exactly  the  same  in- 
stant. If  they  are  not  so  synchronized  the  effect  will  be  that 
of  only  one  magneto. 

EMERGENCY  REPAIRS 

It  sometimes  becomes  necessary  to  make  repairs  of  a  tem- 
porary nature,  in  order  to  keep  an  engine  running.  This  is 
especially  true  of  long  flights.  In  order  to  make  repairs  quickly 
and  intelligently,  the  operator  must  familiarize  himself  with 
the  propulsion  plant  of  the  flying-boat  or  plane  he  is  operating. 

A  complete  kit  of  tools  and  spares  must  be  carried,  and 
the  operator  should  inspect  this  kit  carefully  before  starting 
on  a  long  flight. 

When  in  flight  the  operator  should  pay  particular  atten- 
tion to  the  various  gauges,  tachometer,  oil  and  water  tempera- 
ture gauges,  oil  pressure  gauge,  and  ampere  meter.  These  in- 
struments indicate  at  all  times  the  working  condition  of  the 
engine,  and  a  sudden  change  indicated  on  one  of  these  gauges 
is  invariably  an  indication  of  trouble.  Water-hose  connections 
sometimes  burst  or  get  loose.  This  results  in  a  loss  of  water 
and  overheating  of  the  engine,  and  would  be  indicated  by  the 

49 


water-temperature  meter  showing  a  sudden  increase  of  tem- 
perature. Repairs  can  be  made  by  fitting  a  new  hose  connec- 
tion or  binding  the  broken  one  with  friction  tape.  As  the 
water  has  all  escaped  through  the  broken  connection  it  becomes 
necessary  to  use  sea  water.  Sea  water  can  be  used  in  an  emer- 
gency of  this  kind  in  order  to  get  back  to  the  base  or  station, 
and  the  cooling  system  should  be  thoroughly  flushed  with  fresh 
water  as  soon  as  possible. 

Broken  water  jackets  can  be  repaired  on  some  engines 
by  plugging  the  inlet  and  outlet  water  pipes  of  the  cylinder  and 
disconnecting  the  spark  plug  wires.  This  puts  the  damaged 
cylinder  out  of  service,  and  as  it  could  not  fire  it  would  need 
no  water  circulation. 

On  the  Liberty  engine  using  Delco  ignition,  it  may  become 
necessary  to  start  two  or  more  engines  with  one  battery.  This 
may  happen  with  one  of  the  large  flying  boats  having  two  or 
more  engines,  and  is  brought  about  by  a  battery  becoming  ex- 
hausted or  broken.  In  a  case  of  this  kind,  two  or  more  engines 
can  be  started  by  connecting  one  good  battery  to  the  first  engine 
to  be  started,  and  starting  same.  Speed  this  engine  up  to 
700  r.  p.  m.  and  throw  back  switches  on.  The  battery  generator 
will  then  charge  and  the  battery  can  be  disconnected  and  used 
in  the  same  manner  for  starting  other  engines. 

Temporary  repairs  to  broken  gasoline  pipes  can  be  made 
by  wrapping  with  tape  or  by  slipping  rubber  tubing  over  each 
broken  end  (this  rubber  tubing  is  usually  carried  in  the  kit). 


50 


Valve  timing — 


ENGINE   CHARACTERISTICS 

LIBERTY— 12 

12  Cylinders — Vee  type  angle  between  cylinder  banks  45°. 

Bore — 5  inches. 

Stroke — 7  inches. 

Cooling — Water  circulated  by  a  high  speed  centrifugal  pump. 

Lubrication — Force  feed  dry  sump  external  oil  reservoirs.    Ca- 
pacity, 13  American  gallons. 

Carburetion—2  Zenith  Duplex  model  U.  S.  52. 

Ignition — Delco  battery  type. 

Idling  speed— 650  to  800  r.p.m. 

Intake  opens  10°  PTC. 
Jntake  closes  45°  PBC. 
Exhaust  opens  50°  BBC. 
Exhaust  closes  10°  PTC. 

Spark  full  advance— Occurs          30°  BTC. 

Spark  full  retard— Occurs  10°  PTC. 

Total  spark  movement —  40° 

Spark  plug  gap—  .017" 

Conditions  for  best  results—Water  at  outlet  170°  Fahr.    (Water 
at  outlet  not  to  exceed  200°  Fahr.) 

Oil  temperature  desired — 130°  Fahr.     (Sometimes  goes  to  150° 
Fahr.) 

Oil  pressure — Varies  between  20  Ibs.  and  50  Ibs. 

Generator  charging  rate — With  fully  charged  battery  1.5  to  3 
amperes. 

Firing  order—  1L-6R-5L-2R-3L-4R-6L-1R-2L-5R-4L-3R. 

Vah-e  clearance-  I^e     .014;;  to  .016;;. 
I  Exhaust  .019"  to  .021". 
Breaker  gap— All  contacts  .010"  to  .013". 
Spark  plug  gap—Q.17". 

51 


THE  LIBERTY  ENGINE— MODEL  A 

Timing   gear   end.     Showing   ignition    heads,    generator,   cam 
shaft   drive,   water  pump  and   oil   pump   assembly. 

52 


One  of  the  chief  characteristics  of  the  Liberty  engine  is 
the  use  of  a  45°  angle  between  banks.  With  the  ordinary 
twelve  cylinders  having  an  equal  firing  interval,  the  angle 
used  is  60°.  By  decreasing  this  angle  the  resistance  offered 
by  the  engine  in  flight  is  naturally  decreased.  This  is  a  very 
important  factor,  particularly  where  the  engine  is  incorporated 
in  the  fuselage  itself.  The  use  of  the  smaller  angle  also  makes 
possible  a  more  rigid  construction,  and  better  reinforcement 
of  the  crank  case.  By  the  use  of  the  consequent  unequal  fir- 
ing interval  of  45°-75°  the  resultant  sympathetic  vibration 
produced  approximates  0.  In  any  engine  with  an  even  firing 
interval  this  vibration  is  foumi  to  a  much  greater  extent  and 
as  vibration  is  detrimental  to  the  molecular  construction  of 
the  metals  used,  it  may  be  seen  the  additional  advantage 
derived.  To  illustrate  this  point  more  clearly :  a  body  of  troops 
marching  across  a  bridge  use  "route  step."  If  they  were 
allowed  to  march  "in  step"  there  would  be  serious  danger 
of  collapse  of  the  bridge,  because  of  the  resultant  sympathetic 
vibration. 

The  construction  of  the  cylinders  of  the  Liberty  engine 
follow  to  a  certain  extent  the  methods  used  by  the  Mercedes, 
Benz,  and  other  foreign  manufacturers.  The  cylinder  sleeve 
itself  is  machined  from  a  steel  forging,  the  valve  cages  are 
welded  on,  and  the  water  jackets,  which  are  of  pressed  steel, 
are  welded  to  this  assembly.  The  cylinder  itself  is  forged 
by  a  unique  process  developed  by  the  Ford  Motor  Company — 
a  piece  of  steel,  resembling  a  section  of  boiler  tubing,  is  so 
forged  by  means  of  steam  presses  that  the  finished  product 
is  sealed  at  the  top  upset  to  provide  the  semi-spherical  combus- 
tion chamber,  and  have  a  metal  ring  providing  the  flange  for 
attachment  to  the  crank  case.  By  the  use  of  this  process  the 
expense  of  manufacture  was  greatly  diminished  over  any 
method  heretofore  used,  and  it  was  possible  to  turn  out  well 
over  two  thousand  forgings  a  day.  This  rough  forging  weighs 
approximately  fifty-eight  pounds,  while  the  finished  cylinder, 

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including,  valves  and  valve  springs,  weighs  only  approximately 
twenty  pounds.  From  this  it  is  possible  to  obtain  some  realiza- 
tion of  the  machining  done. 

The  cylinder  extends  considerably  below  the  holding  down 
flange,  giving  increased  strength  to  the  assembly.  The  in- 
formation of  the  combustion  chamber  is  hemispherical  with 
the  valves  and  spark  plugs  located  symmetrically  in  the  head. 
The  cylinder  is  upset  at  the  combustion  chamber,  so  that  am- 
ple clearance  may  be  afforded  for  the  large  valves  used.  The 
outside  of  the  cylinder  is  flanged,  so  that  additional  cooling 
surface  is  provided. 

On  account  of  the  high  compression  used,  it  is  necessary 
to  provide  extremely  efficient  cooling.  This  is  done  by  the 
use  of  a  pump  of  large  capacity  (one  hundred  gallons  per 
minute  at  maximum  speed).  Also  the  water  enters  the  jackets 
at  the  side,  causing  a  swirling  rapid  circulation.  It  also  flows 
freely  over  the  combustion  chamber  and  around  the  valves. 
From  the  top  of  the  jackets  it  enters  jackets  surrounding 
the  intake  manifolds,  so  that  the  incoming  gases  are  heated. 
From  these  manifolds  it  passes  through  the  main  water  heater, 
back  to  the  radiator. 

The  cam  shafts  are  of  the  over  head  type  of  special  and 
improved  design,  being  well  lubricated  and  yet  practically  oil 
tight.  They  are  driven  by  tower  shafts,  which  derive  their 
motion  from  timing  gears  in  the  crank  case. 

The  lubrication  system  is  essentially  one  of  the  forced 
feed  principal.  The  engine  is  of  the  dry  sump  type.  The  oil 
being  carried  in  outside  reservoirs.  It  is  therefore  necessary 
to  supply  two  oil  pumps,  one  for  delivery  of  oil  through  the 
system,  and  one  for  return  back  to  the  reservoirs.  These  two 
pumps  are  of  the  rotary  gear  type,  and  are  both  included  in 
one  assembly.  The  oil  goes  from  the  reservoirs  to  the  delivery 
pump  by  gravity.  From  there  it  goes  past  a  pressure  relief 
valve,  (regulated  to  fifty  pounds  maximum  pressure)  to  the 
main  oil  duct  which  runs  the  length  of  the  engine,  along  the 

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bottom  of  the  sump.  From  this  duct  it  goes  to  the  seven  main 
crank  shaft  bearings,  through  leads  in  the  webbing.  Oil 
enters  the  first  six  crank  journals  and  flows  to  the  crank  pins, 
through  holes  in  the  cheeks.  Thus  lubrication  is  provided  for 
connecting  rod  bearings;  cylinder  walls;  etc.  The  part  of 
this  oil  not  actually  consumed,  falls  back  into  the  sump,  with 
the  propellor  end  of  the  engine  up,  it  flows  direct  to  the  re- 
turn pump,  and  thence  to  the  reservoirs.  With  the  propellor 
end  down  it  collects  in  a  small  well  near  this  end  of  the  sump, 
and  goes  to  the  return  pump  by  means  of  a  suction  duct, 
provided  for  the  purpose.  Part  of  the  oil  is  conducted  around 
the  main  bearing  at  the  propellor  end,  and  goes  through  out- 
side leads,  to  the  cam  shaft.  It  flows  through  these  provid- 
ing lubrication.  From  here  it  flows  down  through  the  cam 
shaft  drive  housings,  over  the  timing  gears,  to  the  return  pump. 

There  is,  practically  speaking,  only  one  difference  between 
the  Liberty  engines,  as  used  by  the  Army  and  Navy.  The 
former  use  a  higher  compression  than  the  latter.  This  is 
accomplished  by  means  of  a  dome  topped  piston,  as  against 
a  flat-topped  piston.  The  horse-power  developed  in  the  low 
compression  engines,  ranges  375-400.  While  that  of  the  high 
compression  is  from  425-450.  The  weight  of  both  engines  is 
approximately  eight  hundred  and  twenty-five  pounds  (825  Ibs.) 
and  the  maximum  speed  from  1650  to  1800. 

The  crank  shaft  used  is  a  drop  forging,  having  seven 
bearings  and  being  two  and  five-eighth  inches  in  diameter. 
The  crank  shaft  bearings  are  carried  in  the  webbing  between 
the  crank  case  and  the  sump;  thus  making  a  very  rigid  con- 
struction, and  giving  better  constructional  alinements. 

The  connecting  rods  are  of  the  "I"  beam  type — twelve 
inches  between  centers.  They  are  of  the  forked  type,  so  that 
no  offsetting  of  the  cylinder  banks  is  required.  The  left  rods 
are  forked,  and  the  right  plain.  The  piston  pin  is  a  seamless 
steel  tube,  and  is  a  drive  fit  into  the  bosses  of  the  aluminum 
piston.  They  are  of  the  full  floating  type,  being  held  in  place 

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by  piston  pin  retainers.  These  are  small  pieces  of  aluminum, 
shaped  to  conform  with  the  piston  surface.  They  are  placed 
in  the  outer  side  of  each  boss,  so  that  while  the  piston  pin 
is  free  to  move,  in  both  the  bosses  and  the  connecting  rod, 
its  lateral  motion  is  constrained.  By  this  method  of  con- 
struction the  danger  of  the  piston  pin  breaking  loose,  and 
scoring  the  cylinder  walls,  is  done  away  with. 

The  following  paragraphs  describing  the  carburetors  used 
in  the  Liberty  engine  are  reprinted  from  an  article  written 
by  the  Zenith  Carburetor  Company. 

"The  carburetors  used  on  Liberty  engines  are  of  Zenith 
manufacture  and  are  of  duplex,  or  double,  type,  and  known  as 
their  Model  US-52.  Each  barrel  is  of  52  mm.  inside  diameter 
and  as  two  carburetors  are  used  on  each  12-cylinder  engine 
there  is,  in  effect,  one  complete  carbureting  chamber  for  each 
three  cylinders." 

"As  synchronism  is  essential,  it  is  necessary  that  each  car- 
bureting chamber  supplies  the  same  amount  of  a  fuel  mixture 
that  is  itself  composed  of  equal  proportions  of  fuel  vapor 
and  air  with  any  given  throttle  openings.  Obviously,  all  four 
throttle  valves  must  operate  in  unison." 

"To  accomplish  this  result  it  is  necessary  that  each  fuel 
orifice  and  choke  tube  shall  deliver  the  same  amount  of  fuel 
and  air  under  a  given  suction.  The  choke  tubes,  commonly 
called  venturi  or  chokes,  are  designed  so  as  to  offer  the  least 
resistance  to  passage  of  the  air,  and  are  therefore  of  a  perfect 
stream  line  in  section.  At  present,  the  carburetor  setting  for 
the  12-cylinder  Liberty  engines  calls  for  a  No.  31  choke.  This 
means  that  the  throat  diameter,  or  the  inside  diameter  of  the 
choke  at  its  narrowest  point,  is  exactly  31  mm.  This  is 
checked  by  the  use  of  "go"  and  "no  go"  ball  gauges,  and  is 
held  accurate  within  limits  of  .006"." 

"The  main  jet  sizes  now  used  are,  for  the  high  compres- 
sion Army  engines,  No.  140,  and  for  the  IOWT  compression 
Navy  engines,  No.  145.  The  jets  are  numbered  according  to 

60 


the  diameter  in  1.100th  of  a  mm.  of  the  fuel  orifice,  and  they 
are  calibrated  and  carefully  gauged  for  size  by  means  of  ac- 
tual flow  of  water  through  them  from  a  height  which  is  kept 
constant  by  an  automatic  level  device  in  the  testing  tank.  The 
testing  is  done  automatically  by  an  electric  and  clock  device 
which  causes  the  water  passing  through  the  jet  to  flow  into 
a  cubic  centimeter  graduate  for  exactly  one  minute,  when  the 
water  is  diverted,  also  automatically,  into  a  drain  for  a  period 
of  l/2  minute  of  time,  during  which  interval  another  jet  is 
placed  in  the  machine  for  testing.  From  experiment  and  cal- 
culation it  is  known  that  a  1  40-100  mm.  jet  will  flow  335  cu. 
cm.  of  water  in  one  minute  from  a  head  of  1  meter.  The 
tolerance  allowable  is  4  cu.  cm.  over  and  1  cu.  cm.  under. 
The  larger  "over"  limit  is  used  because  the  graduate  will  not 
always  be  perfectly  drained.  The  same  method  of  numbering 
and  calibrating  is  used  in  the  case  of  the  compensating  jets. 
The  present  setting  calls  for,  in  the  case  of  the  Army  engine, 
a  Xo.  150  Compensator,  and,  for  the  Navy  engine,  a  No.  155 
Compensator." 

A  starting  and  idling  device  is  incorporated  in  the  con- 
struction of  the  carburetor  which  works  only  when  the  throttle 
valves  are  in  nearly  closed  position.  This  device  consists  of 
the  "idling  tube"  which  is  drilled  at  its  lower  and  with  a  1  mm. 
drill  for  the  measuring  of  the  fuel,  and  at  its  upper  end, 
with  four  1  mm.  holes  for  the  measuring  of  the  air;  and  of 
a  "priming  tube"  which  projects  down  to  about  1  mm.  from 
the  bottom  of  the  "idling  tube,"  and  which  forms  a  passage 
for  the  mixture  of  fuel  and  air  to  the  "priming  hole"  which 
enters  the  carbureting  chamber  at  the  lower  edge  of  the  throttle 
valves.  It  should  be  noted  that,  as  the  relative  position  of  the 
throttle  valve  and  the  priming  hole  determines  the  suction  on 
the  idling  device,  and  consequently  the  quality  of  the  idling 
mixture,  the  throttle  valves  should  all  be  fitted  within  very 
narrow  limits  and  that,  when  completely  closed,  the  top  of 
the  valves  should  just  cover  the  priming  holes.  If  this  point 

61 


is  noted,  it  is  obvious  that  the  throttle  valves  will  all  open 
in  unison  and  thus  be  in  synchronism.  The  wide-open  posi- 
tions of  the  valves  will  take  care  of  themselves  and  are, 
relatively,  not  so  important  as  the  closed  positions.  As  a 
matter  of  fact,  after  the  throttle  valves  are  three-quarters  of 
the  way  open,  further  opening  will  not  have  such  influence 
on.  the  power  or  action  of  the  engine. 

When  the  throttle  valves  are  opened,  the  suction  on  the 
jets  overcomes  the  suction  at  the  priming  holes,  and  the  fuel 
is  therefore  drawn  through  the  jets  and  the  idling  device  is 
automatically  put  out  of  action. 

An  adjustment  is  incorporated  in  the  carburetor  for  the 
purpose  of  conserving  the  fuel  supply  by  taking  advantage  of 
the  lesser  demand  for  fuel  due  to  the  decrease  in  air  density 
met  with  in  higher  altitudes. 

The  purpose  is  accomplished  by  "putting  a  brake"  on  the 
fuel  supply  thru  the  jets.  The  carburetor  fuel  bowl  normally 
has  atmospheric  pressure  existing  within  it,  and  this  pressure 
is  reduced  by  placing  it  in  communication,  thru  a  suitable 
channel  and  adjustable  valve,  with  the  inside  of  the  carburetor 
barrel,  where  a  low  pressure  condition  exists  during  the  run- 
ning of  the  engine.  By  thus  reducing  the  pressure  on  the 
jets,  their  flow  is  decreased  to  a  point  where  it  compensates 
for  the  lesser  weight  of  air  being  drawn  into  the  carburetor, 
a  proper  air-gas  mixture  ratio  is  maintained,  and  wastage 
fuel  eliminated. 

LIBERTY-DELCO  IGNITION  SYSTEM 

The  ignition  system  as  used  on  the  Liberty  engine  is  of 
Delco  design,  and  made  by  the  Dayton  Engineering  Labor- 
atories of  Dayton,  Ohio.  It  is  a  battery  generator  system  and 
primarilly  operates  on  the  principle  of  the  battery  system,  as 
described  previously. 

The    system    consists    essentially    of    six    units,    viz:    two 

62 


THE  LIBERTY  ENGINE— MODEL  B 

Showing  the  incorporation  of  a  reduction  gearing  enabling  higher 
engine  speeds  and  consequently  increased  Horse  Power  Output. 
The  gearing  keeps  the  propeller  speed  down  to  an  efficient  range. 


63 


distributor  heads,  storage  battery,  generator,  switch,  and  volt- 
age regulator.  Both  distributor  heads  are  identical  and  con- 
tain the  breaker  mechanism,  condensor,  induction  coil,  and 
distributor.  The  distributor  segments,  coils  and  secondary 
terminals,  are  encased  in  Baekelite  so  that  they  are  fool  proof. 
Also  the  coils  are  protected  from  dampness  and  consequent 
deterioration.  This  Baekelite  assembly  fastens  to  the  rest  of 
the  head  by  clamps  and  thumb  screws  which  act  as  coil  ter- 
minals. Also  contained  in  the  entire  assembly  are  the  breaker 
mechanism,  condenser,  and  distributor  arm. 

The  battery  supplies  the  current  for  starting  and  is  a 
four  cell  three  volt  storage  type.  The  generator  is  a  four 
pole,  shunt  wound,  direct  current  machine,  so  arranged  that 
at  engine  speeds  of  650  r.p.m.  and  over  it  generates  sufficient 
current  to  supply  ignition  and  charge  the  battery.  The  volt- 
age regulator  is  used  so  that  the  charging  rate  may  be  kept 
constant  and  not  increase  excessively  due  to  the  increase  of 
engine  speeds.  It  operates  on  the  Tyrrel  principle  by  fluctuat- 
ing the  generator  field  strength  rapidly  and  consequently  keep- 
ing the  voltage  output  at  what  may  be  taken  as  a  constant 
value.  The  switch  assembly  is  a  combination  of  two  switches ; 
one  to  control  the  left  hand  distributor  head,  which  is  placed 
on  the  timing  gear  end  of  the  left  hand  cam  shaft;  the  other 
to  control  the  right  hand  head  located  correspondingly  on  the 
right  hand  cam  shaft.  The  switch  is  so  arranged  as  to  con- 
trol the  circuits  to  each  of  the  distributors,  and  generator 
to  battery  circuit.  It  also  includes  an  ammeter  which  has 
proven  very  useful  since  it  tells  the  condition  of  the  ignition 
system  at  all  times. 

The  ammeter  shows  the  charging  rate  of  the  generator, 
or  the  discharging  rate  of  the  battery  whenever  either  or  both 
switches  are  on,  and  at  all  engine  speeds.  Each  distributor 
is  connected  to  give  twelve  sparks  every  two  revolutions  of 
the  crank  shaft,  thus  firing  one  spark  plug  in  each  of  the 
twelve  cylinders.  The  advantage  of  this  is  more  positive  and 

64 


complete  ignition,  providing  both  sparks  occur  at  the  same 
instant,  as  they  must  be  timed  to  do.  This  also  provides  a 
larger  safety  factor,  since  the  engine  will  run  with  only  one 
spark  plug  in  each  cylinder  firing,  the  only  effect  being  a  slight 
drop  in  r.p.m. 

The  breaker  mechanism,  instead  of  having  only  one  set  of 
breaker  points,  has  two  sets,  wrhich  are  arranged  in  parallel 
and  termed  accordingly — the  parallel  breakers.  The  advantage 
is  again  safety  factor  and  the  additional  path  for  current 
flow  when  the  points  are  together  for  an  extremely  short  in- 
terval, as  is  the  case  at  high  engine  speeds.  Naturally  two 
breaker  points  offer  less  resistance  to  the  current  flow  than 
would  one.  The  use  of  the  safety  factor  is  apparent  in  that 
one  set  of  points  may  stick  open,  or  become  entirely  inoper- 
ative for  some  reason,  and  yet  the  other  set  will  carry  the 
load  and  the  engine  will  operate  without  hindrance ;  the  only 
difference  being  a  slightly  less  intense  spark  at  high  speed. 

In  a  battery  ignition  system  the  source  of  current,  being 
always  constant,  will  cause  induction  to  take  place  whenever 
the  primary  circuit  is  broken,  regardless  of  the  direction  of 
rotation,  as  it  is  very  often  necessary,  particularly  when  crank- 
ing by  the  propeller,  to  rock  the  motor.  It  may  be  readily 
seen  that  sane  means  be  used  to  prevent  ignition  occurring, 
so  that  the  danger  of  a  back  kick  may  be  eliminated.  This 
is  accomplished  by  means  of  an  auxiliary  or  third  breaker 
point.  This  is  also  incorporated  in  the  distributor,  and  is  con- 
nected in  parallel  with  the  parallel  breakers.  It  is  so  placed 
and  timed,  so  that  when  the  engine  is  rotated  in  the  proper 
direction  it  will  open  slightly  before  the  main  points,  thus 
causing  no  hindrance  to  the  proper  break.  A  small  resistance 
unit  is  connected  in  series  with  the  third  breaker. 

\Yhen  rotation  in  the  improper  direction  occurs,  the  main 
points  open  first  and  the  third  point  remaining  closed,  pro- 
vides a  connection  to  the  ground.  Due  to  the  resistance  unit 
the  primary  current  is  so  weakened  in  value  that  \vhen  the 

65 


third  point  does  open  the  induction  caused  is  not  strong  enough 
to  produce  a  spark.  It  must  be  noted,  however,  that  this  does 
not  prevent  the  occurrence  of  one  spark  due  to  cranking  with 
the  spark  in  the  advanced  position.  Consequently  it  is  possible, 
as  in  any  engine,  to  obtain  a  back  kick,  if  the  spark  is  not 
retarded  when  starting.  It  is,  however,  impossible  for  counter 
rotation  to  occur  to  more  than  this  extent. 

The  cam  that  operates  the  breakers  has  twelve  lobes,  and 
rotates  at  cam  shaft  speed.  These  lobes  are  spaced  22.5°  and 
37.5°  apart.  This  unequal  spacing  is  brought  about  by  the 
angle  between  cylinder  banks  (45°)  which  causes  unequally 
spaced  power  impulses,  consequently,  unequally  spaced  sparks 
must  be  delivered.  The  battery  is  a  storage  type  having  four 
cells,  its  voltage  when  fully  charged  is  approximately  nine 
volts  and  must  never  be  allowed  to  become  discharged.  The 
battery  is  tested  with  a  hydrometer  syringe,  and  the  specific 
gravity  of  the  electrolyte  should  be  1.280  to  1.310  for  a  full 
charge.  To  test  battery  with  hydrometer,  lay  battery  on  side 
until  electrolyte  has  run  into  the  top  chamber,  then  suck  it  out 
with  hydrometer.  The  battery  is  of  the  non-spillable  type, 
and  differs  from  the  ordinary  automobile  battery  only  in  that 
respect.  As  the  generator  is  only  intended  to  keep  the  bat- 
tery fully  charged,  and  not  to  recharge  a  discharged  battery, 
a  battery  that  shows  a  hydrometer  reading  of  1.225  or  less 
should  be  taken  off  and  charged  from  an  external  source. 

The  generator  requires  no  attention  except  for  an  oc- 
casional oiling. 

The  regulator  has  one  adjustment,  and  should  not  be  in- 
terferred  with.  The  charging  rate  of  the  generator  is  1.5 
to  3  amperes,  and  should  only  be  adjusted  with  a  fully  charged 
battery,  and  by  someone  familiar  with  the  regulator. 

The  switch  contains  the  ignition  resistance  units  which 
are  connected  in  series  with  the  distributors.  The  function 
of  these  resistance  units  is  to  control  the  flow  of  current  when 
the  engine  is  being  started  or  is  running  slow.  If  the  engine 

66 


is  stopped  and  one  switch  is  thrown  on  (either  one),  the 
battery,  is  connected  to  the  distributor  controlled  by  that  switch. 
If  the  breaker  contacts  have  closed,  there  would  be  a  very 
heavy  discharge  of  current,  which  would  soon  weaken  the 
battery.  To  overcome  this  the  resistance  unit  is  used,  and  it 
will  only  allow  a  discharge  of  4  to  5  amperes  (registered  on 
amperes  meter),  which  is  all  the  current  necessary  for  ignition. 

The  engine  is  always  started  with  one  switch  (either  one) 
"on"  and  both  switches  should  not  be  thrown  "on"  until  the 
engine  is  running  650  r.p.m.  or  faster.  With  one  switch 
on  the  battery  is  supplying  the  current,  and  the  ampere  meter 
will  show  a  discharge;  with  both  switches  on  and  an  engine- 
speed  of  650  r.p.m.  or  faster,  the  generator  is  supplying  the 
current,  and  the  ampere  meter  will  show  "charge."  It  can  be 
seen  from  the  above,  that  with  both  switches  on  and  an 
engine-speed  of  less  than  650  r.p.m.,  the  battery  would  be 
supplying  the  current  for  both  distributors,  and  that  the  battery 
would  also  be  discharging  through  the  generator.  The  result 
would  be  a  heavy  drain  on  the  battery,  which  would  soon 
result  in  its  being  damaged,  or  completely  exhausted.  Con- 
ditions such  as  this  are  always  indicated  by  a  heavy  "dis- 
charge" on  the  ampere  meter  and  should  be  avoided  by  throw- 
ing "off"  one  switch. 

In  order  that  the  operation  of  the  switch  may  be  made 
clear,  a  diagram  showing  three  positions  of  the  switch  is 
shown  on  the  preceding  page. 

Figure  1  shows  the  right  switch  in  the  position  "on" 
for  starting.  The  right  switch  moves  the  two  blades  G,  and 
H,  on  and  off  the  three  contacts.  These  two  blades  are  con- 
nected together.  It  can  be  seen  that  current  will  flow  from 
the  battery  connected  at  A,  through  the  ampere  meter,  then 
through  the  two  blades,  and  out  through  the  resistance  unit 
(crooked  line)  to  the  right  distributor  connected  at  D. 

67 


68 


Figure  2  shows  the  left  switch  in  the  position  "on"  for 
starting,  and  the  same  conditions  prevail  as  in  figure  1.  ex- 
cept that  the  two  blades  E,  and  F,  are  insulated  from  each 
other,  so  that  current  flows  through  each  blade  independent 
of  the  other.  It  will  be  noticed  in  figures  1  and  2  that  the 
ampere  meter  shows  a  discharge  of  approximately  4.5  amperes. 
The  meter  should  always  have  a  discharge  of  approximately 
4.5  amperes,  with  engines  stopped  and  one  switch  "on"  pro- 
vided the  breaker  points  in  the  distributor  are  closed. 

Figure  3  shows  both  switches  "on/'  and  the  meter  indi- 
cating "charge."  This  condition  is  indicated  for  engine  speeds 
of  over  650  r.p.m.  as  the  generator  is  now  supplying  the 
current.  The  generator  circuit  is  completed  from  C  through 
the  blade  F  to  blade  H,  from  this  blade  the  current  can  be 
traced  to  both  distributors  and  to  the  batterv. 


69 


70 


71 


ORDER  OF  TEARDOWN 

U.   S.   N.   LIBERTY  MOTOR   SCHOOL 

1.  Distributor  head  and  high  tension  wire  conduit. 

2.  Drain  all  oil. 

3.  Distributor  mechanism. 

4.  Oil  pipes. 

5.  Camshaft  assembly. 

6.  Generator. 

7.  Mark  carburetor  and  intake  headers. 

8.  Water  pipes  and  hose. 

9.  Breathers. 

10.  Carburetors. 

11.  Intake  headers. 

12.  Propeller  hub. 

13.  Cylinders. 

14.  Oil  pump  assembly  and  pump  cover. 

15.  Water  pump  assembly. 

16.  Two  camshaft  drive  shaft  gear  assembly. 

17.  Oil  pump  driving  gears. 

18.  Water  pump  driving  gears  and  shaft  assembly. 

19.  Piston  pin  retainers. 

20.  Pistons. 

21.  Upper  half  crankcase. 

22.  Crank  assembly. 

23.  Connecting  rods  and  thrust  bearing. 

NOTE:  Each  part  to  be  thoroughly  oiled  to  resist  rust,  and 
each  part  (where  there  is  opportunity  of  mixing  up)  to  be 
tagged. 

72 


TEARDOWN 

U.  S.  X.  LIBERTY  MOTOR  SCHOOL 

1— DUAL  IGNITION  SYSTEM: 

(a)  Each  distributor  fires  one  plug  in  each  cylinder  through- 
out entire  cylinders. 

(fr)  Right  distributor  fires  plugs  on  gear  side  of  cylinder 
while  the  left  fires  the  propeller  side. 

(c)  Disconnect  high    tension  conduit  which  is  attached  to 
outlet  water  header  by  cap  screws  with  no  washers. 

(d)  Remove  the  twelve  insulated  wires  fastened  to  spark 
plugs,  being  careful  not  to  spring  ball-clips.     Rubber 
ferrules  on  end,  must  be  in  perfect  condition  to  assure 
perfect  insulation. 

(c)  Remove  distributor  heads  held  by  wire  clips  along  with 
the  conduit.  Care  should  be  taken  to  bind  the  brushes 
with  a  rag  or  rubber  band  to  prevent  any  breakage. 

2— CAMSHAFT  HOUSING  ASSEMBLIES  : 

(a)   Remove  distributor  tie  rod  found  in  upper  holes  with 

boss  down. 
(6)   With    spanner    wrench    remove    collars    on    camshaft 

housings.     A  felt  washer  should  be  inserted  in  each 

collar  to  prevent  oil  leakage. 

(c)  Loosen  castle  nuts  on  the  twelve  studs  of  each  cam- 
shaft housing.     Plain  washers  arc   found  under  each 
nut. 

(d)  Disconnect  oil  pipes  leading  to   camshaft  before   re- 
moving camshaft  assemblies  which  are  marked  either 
right  or  left. 

(f)   Male  splines  on  jack-shaft  marked  by  a  groove  in  one 

tooth. 
(f)   Female  spline  carried  two  niches  on  collar.  Both  splines 

must  coincide  for  timing. 

73 


3— GENERATOR: 

(a)   Held  by  three  castle  nuts  on  studs.    Plainwashers.    Oil 
paper  gaskets  are  found  between  generator  pad  and  scat. 
(fr)   Only  one  bearing  in  generator. 

(c)  Power  connections  not  marked. 

(d)  Splines  must  fit  closely  to  prevent  any  back  lash  (conic 
out  rather  hard). 

4— CARBURETORS : 

(a)  Unfasten  carburetor  tie-rod.     Purpose  of  rod  to  make 
carburetors  work  simultaneously. 

(b)  Watch  taper  pins  that  lock  tie-rod. 

(c)  Be  careful  of  pins.    Easily  lost. 

(d)  Two  copper  asbestos  washers  separate  each  carburetor 
from  manifold. 

(c)  Although  interchangeable,  mark  each  carburetor  pro- 
peller end  and  gear  end. 

(/)  Each  carburetor  held  by  two  anchor  bolts  with  plain 
washer  fastened  to  hot  water  intake  header. 

5— HOT  WATER  INTAKE  HEADER: 

(a)  Held  by  four  castle  Huts  with  washers   at  each  end, 
having  also  two  oil  paper  gaskets. 

(b)  This  parts,  with  carburetor,  removed  practically  at  the 
same  time,  holding  one  in  each  hand. 

6— MANIFOLD  OR  INTAKE  HEADERS: 

(a)  Four  in  number,  each  held  by  six  studs,  castle  nuts  and 
washers,  paper  gaskets  between  each. 

(b)  Each  manifold  stamped  on  exhaust  port  flange — pro- 
peller end  R.  or  L.  and  gear  end  R.  or  L.  as  the  case 
may  be. 

(c)  Remove  that  manifold  with  with  smallest  bearing  sur- 
face first.     Found  hire  to  be  right  side. 

(d)  Inspect  manifolds  for  loose  cores  which  rattle. 

74 


7— WATER  SYSTEM: 

(a)  Remove  both  outlet  water  pipes  from  pump.     Right 
side  is  longer  than  left. 

(b)  Remove    inlet   water   headers;    both    pipes   are    inter- 
changeable (hose  hands). 

(c)  Remove  outlet  water  pipes  of  cylinders.     Loosen   all 
hose  bands  attached  to  cylinder. 

(d)  Three  flanges  attached  to  each  manifold  and  held  there 
by  two  cap  screws  through  each  flange  having  driller 
heads    (paper    gaskets    between    manifolds    and    each 
flange). 

(e)  Centrifugal  water  pump  held  by  four  studs  with  castle 
nuts.    Paper  gaskets  separate  pump  pad  and  seat. 

(/)   Pump  intake  points  to  the  left,  plugged  hole  found  at 
the  bottom. 

8— BREATHERS  (CRANKCASE)  : 

(a)  Held  by  two  studs  washers  and  castle  nuts,  has  paper 
gasket  between,  also  baffle  plate  screen. 

(b)  On  propeller  end  the  three  way  distributor  for  oil  fast- 
ened by  two  castle  nuts,  washers  and  has  an  oil  paper 
gasket. 

9— CYLINDERS  (12): 

(a)   Start  from  gear  or  propeller  end  and  remove  flange 

nuts  between  each  cylinder.    Six  other  castle  nuts  serve 

to  hold  skirt  flange  to  cylinder  pad. 
(fr)   Paper  gaskets  between  cylinder  pads  and  flanges  are 

cut  to  cover  three  cylinders. 

(c)  Remove  one  spark  plug  before  pulling  cylinder  off  pis- 
ton to  relieve  vacuum. 

10— PISTONS: 

(a)   Bind  studs  at  base  of  cylinder  pad  to  prevent  scratch- 
ing of  pistons. 

75 


(b)  With  pliers  remove  piston  pin  retainers. 

(c)  Drive  out  piston  with  brass  plug,  pounding  it  gently. 

(d)  Piston  pin  should  only  he  driven  far  enough  to  clear 
pin  housing. 

(e)  Each  piston  is  marked  right  or  left  and  its  numerical 
position. 

(/)   Allow  rings  in  grooves  to  remain  untouched. 

(g)   Rings  are  common  split  type  with  two  right  and  one 

left.     The  splits  being  set  at  180  degrees  apart. 
(/*)   While  removing  piston  pin,  hold  piston  firmly  so  as  not 

to  throw  connecting  rods  out  of  line. 

11— GENERATOR  AND  CAMSHAFT  ASSEMBLIES: 

(a)  Remove  gear  case  cap  held  by  six  cap  screws  drilled 
for  wiring,  no  washers. 

(b)  Remove  jackt  shaft  assemblies  held  by  four  studs  and 
castle  nuts. 

(f)  Should  have  a  paper  gasket  between  crank  case  and 
pad. 

(d)   Each  shaft  marked  right  or  left  on  the  beveled  gear, 
(r)    Ball  race  retainers  in  assembly. 

(/)   These  shafts  must  be  removed  before  generator  shaft, 
as  gears  of  former  prevent  removal  of  latter. 

REMOVE  GENERATOR  DRIVE  SHAFT: 

(a  )   Duty:   to  drive  generator  and  two  jack  shafts. 

(b)  Construction:    With  key-way  in   shaft  for  jack  shaft 
gear  and  two  spacing  sleeves  to  hold  it  where  it  belongs. 

(c)  Bevel  gear  has  twenty-two  teeth. 

12— TIMING: 

(a)  When  No.  1  and  No.  6  are  10  degrees  past  dead  center, 
splines  should  be  placed  in  line  with  center  of  cylinder. 

76 


13— REMOVAL  OF  LOWER  CRAXKCASE: 

(a)  Loosen  fourteen  nuts  on  anchor  bolts,  a  plain  washer 
is  found  beneath  each. 

(b)  Turn   crankcase   over   allowing   an    anchor   flange    to 
rest  on  wooden  blocks  mounted  on  frame. 

(c)  Remove  two  through  bolts  on  each  end  of  base.     Also 
two  anchor  bolts  nuts  were  found  at  propeller  end  and 
removed.     Remove  oil  pump  held  by  ten   castle   nuts 
with  washers.    A  paper  gasket  found  between. 

(J)   Remove  fifty  hexagon  head  holding  upper  and  lower 
crankcases  together. 

(e)  Lift  off  lower  part  of  crankcase. 

14— REMOVAL  OF  SPOOL  GEAR: 

(a)  Loosen  set  screw  which  holds  assembly  in  place. 

(b)  With  case  upright  drive  assembly  through. 

(c)  Upon  measuring  it  it  is  found  to  be  tapered  .0007"  over 
a  distance  of  2y2". 

15— FORK  AXD  PLAIX  EXD  COXXECTIXG  RODS: 

(a)   End  play  of  connecting  rod  allowed  .006",  found  to  be 
as  great  as  .016". 

(6)   Babbitt    metal    bearing    surface    on    fork    rods- 
bronze  on  plain  end. 

REASOX : 

(f )  Plain  end  rod  is  removed  first  by  turning  shaft  to  allow 
it  to  let  go  easily  upon  removing  nuts. 

(</)    Forked  rods  followed,  care  being  taken  to  place  both 
halves  of  bearing  surface  as  they  originally  were. 

16— UPPER  HALF  CRANKCASE: 

(a)   Ispect  bearing  surfaces — high   spots  shows  up  bright 

(should  be  a  lead  color  throughout). 
(6)   Watch  studs  for  loosening  up. 
(c)   Care  should  be  taken  to  find  any  cracks  or  sand  holes. 

77 


CRANKSHAFT  INSPECTION: 

(a)   Inspect  crank  pins  and  main  bearings  for  any  scratches 
or  rough  spots. 
(Crocus  cloth  will  remove  any  slight  scratches.) 

(&)   Teeth  of  driving  gear  on  gear  flanges  should  be  per- 
fect and  not  chewed  up. 

(Pricked  punched  12  degrees  30'  past  center  for  timing 
purposes). 

17— CAMSHAFT  ASSEMBLY: 

(a)  Remove  the  six  plates  holding  rocker  arms  in  place, 
held  by  3  hexagonous  bolts  and  plain  washers. 

(b)  Withdraw  bearing  retainers  which  are  set  screws  used 
to  hold  bearings  in  place. 

(c)  Remove  oil  cap  on  gear  end  with  a  spanner  wrench. 

(d)  Remove    6    hexagonous    nuts    which    hold    distributor 
flange  in  place. 

(c)   Withdraw  camshaft  with  bearings  attached. 

(/)   Split  bearing  surface  held  by  set  screws — bearings  are 

aluminum  throughout  except  at  gear  end,  which  is  a 

bronze  bearing. 


78 


HISPANO  SUIZA 

MODEL  "A" 

8  Cylinders — Ycc  type.    Angle  between  cylinder  banks  90°. 

Bore — 4.72  inches.     Stroke  5.11  inches. 

Horse-power — 150  at  1,450  r.p.m. 

Cooling — Water  circulated  by  a  centrifugal  pump. 

Lubrication — Force  feed. 

Carburetion— Zenith  Duplex  Model  48  D.  C. 

r      •,•  fl  Exciter  magneto. 

hnntwn —  {_  ,  ,    ,  .  „,_. 

12  Dixie  magnetos  Model  800. 

Intake    opens     10°  PTC. 

IT*      T:^:nfl        Intake     closes     50°  PBC. 

Valve  liming —  _0  —.^^ 

Exhaust  opens  4^°  BBC. 

Exhaust  closes  10°  PTC. 
Spark  occurs— 20°  20'  BTC. 
Conditions  for  best  results— Water  at  outlet  165°  to  175°  Fahr. 

Oil  temperature  130°  Fahr. 
Firing  order—  1L-4R-2L-3R-4L-1R-3L-2R. 
Oil  pressure — When  fitted  with  a  relief  valve  can  be  varied  and 

is  usually  about  60  Ibs.  per  square  inch. 
Valve  clearance— .0787" '. 
Breaker  gap—       .020". 
Spark  plug  gap— .020". 

Two  of  the  oustanding  features  of  this  engine  are  the  cyl- 
inder construction,  and  cam  action. 

There  are  two  blocks  of  four  cylinders  each,  here  again 
the  steel  sleeve  is  used.  These  sleeves  are  threaded  on  the  out- 
side, and  four  of  them  screwed  into  an  aluminum  casting  which 
forms  the  water  jacket.  This  gives  a  very  light  assembly  and 
one  which  lends  itself  particularly  well  to  stream  lining. 

The  cam  shafts  are  driven  in  practically  the  same  way  as 
on  the  Liberty,  but  no  rocker  arms  are  used.  The  valve  stems 
are  fitted  with  circular  steel  pieces  which  screw  into  them, 

79 


THE  HISPANO  SUIZA  ENGINE 
MODEL  XE— 300  H.  P. 

Showing  the  stream  line  effect  obtained  by  the  en  bloc  construction 
of  the  water  jackets  and  the  method  used  in  housing  the  cam  shafts. 
The  constructional  features  of  this  model  are  very  similar  to  all 
other  models  of  the  same  engine. 

80 


against  the  action  of  the  valve  spring.  These  are  called  mush- 
rooms, and  the  valve  clearance  is  adjusted  by  screwing  these 
in  or  out.  The  cam  shaft  is  held  on  the  top  of  the  cylinder 
blocks,  by  three  bronze  bearings.  The  cams  themselves  act 
direct  on  the  mushrooms,  so  that  there  is  absolutely  no  lost 
motion.  There  is  an  almunium  cover  which  encloses  the  cam 
shafts,  and  again  very  good  stream  lining  is  accomplished. 

Each  block  of  cylinders,  after  assembly,  are  given  several 
coats  of  enamel,  both  inside  and  out,  each  coat  being  thoroughly 
baked  on.  The  lower  end  of  each  cylinder  projects,  and  has  a 
flange,  by  means  of  which  the  blocks  are  fastened  to  the  crank 
case. 

The  pistons  are  ribbed  aluminum  castings,  provided  with 
four  rings  each,  in  two  grooves  at  the  top.  The  piston  pins  are 
hollow,  and  are  made  of  alloy  steel — case  hardened.  They  are 
held  in  the  piston  bosses  by  means  of  a  single  long  set  screw, 
which  passes  entirely  through  them. 

The  crank  shaft  is  of  the  regular  four-cylinder  type,  that 
is,  having  four  throws,  180°  between  throws.  It  is  of  chrome 
nickel  steel  and  provided  with  four  bearings  of  the  regulation 
bronze  backed,  babbit  lined  type.  In  addition  to  this  there  is 
an  annular  ball  bearing  at  the  cranking  end.  A  double  row  ball 
thrust  bearing  is  located  at  the  propeller  end.  The  crank  shaft 
is  bored  hollow  for  lightness  and  for  oiling. 

The  connecting  rods  are  made  of  heat  treated  alloy  steel, 
and  are  tubular  in  section,  they  are  of  the  forked  type,  as  in 
the  Liberty,  and  carry  a  bronze  bushing  in  the  upper  end.  The 
crank  shaft  bearings  are  carried  in  the  webbing  of  the  crank 
case  and  sump,  as  in  the  Liberty.  The  sump  is  fastened  to 
the  crank  case  by  bolts  running  through  the  webbing  and 
also  by  a  series  of  bolts  around  the  outer  edges.  All  joints  are 
lapped,  that  is;  no  gaskets  are  required. 

Lubrication  is  of  the  force  feed  type.  Pressure  is  provided 
by  a  sliding  vein  eccentric  pump.  Oil  is  carried  in  the  sump. 
The  pump  is  mounted  in  the  sump,  directly  below  the  crank 

81 


shaft  gear.  From  the  pump  the  oil  goes  through  a  removable 
screen  filter,  to  the  main  oil  duct,  from  this,  to  three  of  the 
main  bearings,  thence  through  the  hollow  crank  shaft,  to  the 
four  crank  pins,  lubricating  the  connecting  rod  bearings,  and 
by  spray,  the  piston  pins,  cylinder  walls,  etc.  Oil  is  led  up  to, 
and  around  the  fourth  main  bearing,  from  there  it  goes  through 
outside  leads,  to  the  hollow  cam  shafts.  It  passes  through  these, 
lubrication  being  provided  by  a  small  hole  in  each  cam  surface. 
From  the  cam  shafts  it  returns  to  the  sump,  passing  through 
the  cam  shaft  drive  housings,  and  over  the  timing  gears.  It 
also  lubricates,  on  its  return,  the  crank  shaft  ball  bearings. 

Ignition  is  provided  by  two  8-cylinder  type  Dixie  magnetos, 
firing  one  spark  plug  in  each  cylinder.  One  magneto  is  driven 
from  each  of  the  two  vertical  shafts.  Small  bevel  pinions  mesh 
with  bevel  gears  on  each  magneto  shaft.  No  packing  is  neces- 
sary to  prevent  loss  of  oil  at  these  points.  The  oil  is  prevented 
from  escaping  by  grooves  out  in  the  housings.  The  magnetos 
are  of  the  set  spark  type,  ignition  occurring  at  20°  20'  before 
T.  D.  C.  For  this  reason  it  is  necessary  to  provide  a  distributor 
which  has  two  brushes,  one  for  running  ignition,  the  other  for 
starting.  When  starting  ignition  is  provided  by  a  separate  hand 
exciter,  this  gives  a  shower  of  sparks  to  the  second  on  starting 
brush.  This,  in  effect,  is  the  same  as  a  greatly  retarded  spark. 
Before  starting  it  is  well  to  turn  the  engine  over  a  few  times, 
with  all  ignition  off,  in  order  that  a  good  charge  may  be  taken 
into  each  cylinder. 

For  use  on  sea  planes,  a  geared  down  hand  crank  is  pro- 
vided. In  this  event  the  exciter  is  geared  to  the  starting  crank. 

Carburetion  is  provided  by  a  double  jet  Zenith  carburetor 
model  No.  48  D.  C.  It  is  very  similar  in  construction  and  op- 
eration to  the  Model  U.  S.  52,  used  in  the  Liberty.  The  intake 
manifold  is  water  jacketed  and  runs  crosswise  between  the  cyl- 
inder blocks. 

Cooling  is  provided  by  means  of  water  circulated  by  a 
centrifugal  pump,  which  is  located  at  the  cranking  end  of  the 
engine,  under  the  sump. 


CURTISS 
MODEL  OXX6 

8  Cylinders — Vee  type.    Angle  between  cylinder  banks  90°. 

Bore — 4.25  inches.    Stroke  5  inches. 

Horse-power — 100,  at  1,400  r.p.m. 

Cooling — Water  circulated  by  a  centrifugal  pump. 

Lubrication — Force  feed. 

Ignition — Two  Dixie  magnetos. 

Carburetion — Zenith  Duplex. 

Intake     opens       1/16"  PTC. 


Valve  Timing — . 


Intake    closes        1/2"     PBC. 


Exhaust   opens    13/16"  BBC. 
Exhaust   closes     1/32"  PTC. 
Ignition  occurs — Full  advanced  BTC. 
Firing  or der—l -2-3-4-7-8-5-6-. 
Valve  clearance — .010". 
Breaker  gap—       .020". 
Spark  plug  gap—.Q2Q". 

The  Curtiss  O  X  and  O  X  X  engines  are  probably  the  most 
widely  known  and  used  of  any  in  the  American  field.  The  O  X 
is  the  army  type  and  is  of  four  inch  bore  and  five  inch  stroke, 
while  the  O  X  X  or  Navy  type  differs  only  in  that  its  bore  is 
four  and  one-quarter  inches. 

The  cylinders  are  steel  sleeves  surrounded  by  water  jackets 
of  Monel  metal.  They  are  constructed  separately  and  fasten 
to  the  crank  case  by  means  of  a  flange,  secured  by  studs,  and 
also  by  four  long  studs  which  extend  the  height  of  the  cylinder 
and  fasten  to  a  bracket  at  the  top. 

The  engine  is  provided  with  one  cam  shaft,  located  in  the 
crank  case.  The  valves  are  located  in  the  heads  of  the  cylin- 
ders, the  cam  action  being  conveyed  by  the  rocker  arms,  and 
push  rod  method.  As  applied  to  this  model  engine,  the  particu- 
lar valve  action  may  be  called  characteristic.  The  exhaust  valve 
is  operated  in  the  regular  manner  as  applied  to  an  action  of 

83 


THE   CURTISS   MODEL   OXX   ENGINE 

Showing  the  Push  and  Pull  Rod  type  of  valve  operating  mech- 
anism and  general  assembly.  Note  the  location  of  the  carburetor 
which  facilitates  gravity  feed. 


84 


this  type.  In  other  words,  when  the  high  point  or  toe  of  the 
cam  is  up,  the  push  rod  rises  and  the  rocker  arm  forces  the  valve 
off  the  seat.  It  is  the  operation  of  the  intake  valve  which  dif- 
fers from  conventional  practice.  It  may  be  said  to  be  operated 
by  the  pull  method.  The  intake  cam  is  split,  being  on  either 
side  of  the  exhaust  cam,  the  intake  cam  follower  is  held  on  the 
cam  surface  constantly  by  spring  action.  There  is  a  hollow  rod 
surrounding  the  exhaust  push  rod.  The  lower  end  of  this  rod 
rides  on  the  intake  cam  follower  while  the  upper  end  is  at- 
tached to  the  intake  rocker  arm.  By  spring  action,  which  is 
very  strong,  the  intake  valve  is  forced  off  the  seat  when  the 
cam  follower  is  on  the  low  point  or  heel  of  the  intake  cam. 
When  it  is  on  the  toe  of  the  cam,  the  rocker  arm 'is  held  up, 
away  from  the  valve  stem,  and  the  valve  is  closed.  The  greatest 
advantage  of  this  valve  action  is  economy  of  space. 

The  pistons  are  aluminum  castings,  and  the  hollow  steel 
piston  pins  are  secured  by  a  set  screw  in  one  piston  boss. 

The  crank  shaft  has  four  throws  180°  apart,  and  is  sup- 
ported by  five  main  bearings  of  the  bronze  backed  babbit  lined 
type.  Half  of  each  bearing  is  carried  in  the  webbing  of  the 
crank  case  while  the  other  half  is  carried  in  a  bearing  cap 
which  is  bolted  to  the  crank  case  webbing,  thus  securing  the 
crank  shaft.  This  construction  makes  possible  the  dropping  of 
the  sump,  without  interfering  with  the  support  of  the  crank 
shaft. 

The  connecting  rods  are  heated  treated  drop  forgings  of 
the  I  section  type.  They  fasten  side  by  side  on  each  crank  pin. 
It  is  therefore  necessary  to  set  one  bank  of  cylinders  ahead  of 
the  other. 

The  lubrication  system  is  of  the  forced  feed  type.  The 
sump  is  the  reservoir  and  carries  a  sight  gauge,  and  is  so  con- 
structed that  its  center  is  always  the  lowest  point.  Two  baffle 
plates  are  provided,  which  slope  from  the  ends  of  the  sump 
towards  the  center,  and  leave  a  three-quarter  inch  opening  at 
that  point.  This  opening  extends  the  width  of  the  sump.  A 

85 


rotary  gear  pump  is  located  in  the  low  point  of  the  sump.  Oil 
from  this  goes  to  the  hollow  cam  shaft,  lubricating  its  bearings, 
thence  through  leads  to  the  crank  shaft  bearings,  through  the 
hollow  crank  shaft,  to  the  crank  pins,  lubricating  the  connecting 
rod  bearings,  and  by  spray  the  piston  pins,  cylinder  walls,  etc. 
The  timing  gears  and  thrust  bearing  are  lubricated  by  spray. 
A  pressure  relief  valve  is  located  in  the  line.  On  returning, 
oil  flows  over  the  baffle  plates  and  into  the  sump. 

Ignition  is  provided  by  two  8-cylinder  Dixie  magnetos, 
located  at  each  end  of  the  crank  case,  between  cylinder  banks. 
Each  magneto  fires  are  spark  plugs  in  each  cylinder.  They 
are  provided  with  an  advance-retard  lever. 

Carburetion  is  provided  by  a  Zenith  double  jet  carburetor, 
operating  on  the  regular  Zenith  principle.  It  is  located  at  the 
timing  gear  end  of  the  engine,  below  the  sump.  The  gases  are 
conducted  to  the  cylinders  by  means  of  long  manifolds  which 
are  water  jacketed  at  the  lower  ends. 

The  cooling  system  is  of  the  ordinary  type,  water  being 
circulated  by  a  centrifugal  pump  which  is  located  at  the  timing- 
gear  end  of  the  engine,  on  a  level  with  the  crank  shaft. 

MATERIALS    OF   CONSTRUCTION 

The  following  is  given,  as  an  outline,  setting  forth  briefly, 
the  general  types  of  material  used  in  the  construction  of  the 
present  day  aviation  engine. 

Cylinder:  Cast  iron  is  sometimes  used  where  economy  of 
weight  is  not  so  essential.  When  it  is  used  the  water  jackets 
are  ordinarily  cast  integral  with  the  cylinders. 

Where  economy  of  weight  is  important,  a  sleeve  of  heat 
treated  alloy  steel  is  used.  With  this  type  of  construction  the 
water  jacket  is  made  of  pressed  steel,  and  welded  on,  as  in  the 
Liberty,  or  the  sleeve  is  fitted  in  an  aluminum  block,  as  in  the 
Hispano  Suiza. 

Piston:   Aluminum,  cast  iron  and  semi-steel  are  used.     The 

86 


first  is  the  most  common,  not  only  on  account  of  lightness,  but 
because  of  its  better  heat  conductivity. 

Piston  pin:  Drop  forging  of  alloy  steel,  hollowed  out,  heat 
treated,  and  case  hardened. 

Connecting  rod:  Drop  forging  of  alloy  steel,  often  of 
chrome  nickel  composition,  usually  of  "I"  beam  action  and  ma- 
chined all  over. 

Piston  Rings:  Cast  iron,  used  because  it  is  softer  than  steel, 
and  will  not  scratch  the  cylinder  walls. 

Valves:  Drop  forgings,  usually  of  Tungsten  steel,  and  heat 
treated.  The  presence  of  Tungsten  gives  steel  the  power  to 
withstand  enormous  strains,  even  up  to  cherry  red  heat 

Crank  Shaft:  Drop  forging  of  chrome  nickel  steel,  heat 
treated  and  machined  all  over.  The  presence  of  chromium  en- 
ables steel  to  withstand  the  succession  of  hammer  like  blows, 
while  nickel  increases  the  tensil  strength. 

Cam  Shaft:  Drop  forging  of  heat  treated  alloy  steel,  with 
cams  forged  on  the  shaft  and  their  surface  case  hardened. 

Crank  case  and  Sump:  Aluminum  castings,  ribbed  for 
strength,  and  to  provide  bearing  surfaces. 

Bearings:  Usually  bronze  backed,  Babbit  lined.  Babbit  is 
a  metal  composed  of  antimony,  lead  and  tin,  and  has  a  low 
melting  point.  Used  at  friction  points,  so  that  if  heat  becomes 
excessive,  the  Babbit  will  melt  and  prevent  injury  through 
seizure. 

Bushings:  Usually  bronze.  Used  at  points  of  wear,  so  that 
they  may  be  easily  taken  out  and  replaced,  without  the  neces- 
sity of  providing  large  and  expensive  parts= 


87 


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92 


INDEX 


Page 

Advanced  Spark 47 

Reasons  for 4< 

Effects  of 4i 

Advanced  Timing   4^ 

After  Firing 15 

Causes  of 34 

Air  Bled  Jet 32 

Air  Cooling 22 

Air  Gap 3! 

Altitude  Adjustment 30 

Reasons  for 31 

Effects  of    31 

Aluminum  Pistons 86 

Angle  Between  Banks 21,  53 

Ammeter 64 

Ampere    35 

Armature 41 

Auxiliary  Air  Valve 2» 

Babbit  87 

Back-fire,  Definition  of 15 

Causes  of 34 

Back  Kick 15 

Bakelite  64 

Battery  Ignition  36,  62 

Bearing  11 

Construction  of 87 

Berling  Magneto 41 

Bore  14 

Bosch  Magneto  41 

Breaker  Cam  38 

Breaker  Mechanism  37 

Breaker  Points  38 

Adjustment 39 

Bushing 11 

Construction  of   87 

Cam  Shaft   .  ..11-14 

Cap  Jet    29 

Carburetion     2fi 

Carburetor,    Curtiss    86 

Hispano-Suiza    82 

Liberty    60 

Master   32 

Miller 32 

Model  48  D.  C 82 

Model  U.  S.  52 60 

Simple    26 

Stromberg 32 

Zenith    26,60 

Centrifugal  Pump 23 

Circuit    .  . .   37 


Page 

Coil,   Induction    37 

Primary 37 

Secondary   37 

Combustion  Chamber 3h 

Compensator    27 

Compound  Xozzle 27 

Compression 16 

Condenser 38 

Failure  of   31) 

Conductor 35 

Connecting  Rod 10,  14 

Construction  of   87 

Construction,  Materials  of 8<> 

Contact    15 

Cooling    22 

Cooling  System   ~'-> 

Temperature  of   23 

Crank   Case,   Definition  of 14 

Construction  of 87 

Crank  Shaft 11-14 

Construction  of 87 

Rotation,  Degrees  of 45 

Curtiss  Engine 83 

Cam  Shaft S3 

Carburetion    86 

Connecting  Rod 85 

Cooling    86 

Crank  Shaft   85 

Cylinder     83 

Ignition 86 

Lubrication 85 

Pistons 85 

Specifications  of 83 

Valve  Operation    83 

Cycle    14 

Beginning  of 16 

Four  Stroke   15 

Principle  and  Operation  of 15 

Cylinder,    Purpose   of 10-11 

Construction  of 86 

Dead  Center 14 

Delco  Ignition   62 

Ammeter 64 

Battery 64 

Breaker  Mechanism   65 

Breaker  Points    65 

Cam    66 

For  Running    67 

For  starting   67 

Generator    64 

Regulator    64 

Resistance 66 

Switch    67 


93 


INDEX— Continued 


Page 
Dielectric  .......................    38 

Direction   of   Rotation,    Determina- 
tion of    .......................   46 

Distributer    .....................   40 

Segments  .....................   40 

Arm    .........................   40 

Dixie  Magneto  ..................   42 

Diagram  of  ...................   43 

Sparks   per    Revolution  .........   42 

Speed  of  Rotation  ..............   42 

Dry  Sump  ......................    24 

Advantages  of  ...............  24-25 

Reasons  for    ..................   24 

Duct,  Main  .....................    24 

Oil    ..........................   24 

Eight  Cylinder  Arrangement  ......  21 

Electricity  ......................  35 

Electro-Magnet    .................  35 

Electrode  .......................  36 

Emergency  Repairs  ..............  49 

Engine   Characteristics,   Liberty...  51 

Curtiss  .......................  83 

Hispano-Suiza    ................  79 

Exhaust  Flame,  Color  of  .........  34 


Exhaust  Stroke 

Failure  of  Condenser 

Firing  Order,  Determination  of .  .  . 

Curtiss 

Hispano-Suiza    

Liberty 

Flame,  Exhaust 

Float  Chamber  . 

Flux ; ; ; ; ; 

Reversal  of 38 

Force  Feed  Oiling   

Force  Lines  of 

Four  Stroke  Cycle 

Frequency     

Full  Force  Feed 

Geared  Propeller  Drive 

Generator  Delco    

Ground     

High  Frequency   

Hispano-Suiza  Engine   .  , 

Cam  Shaft 

Carburetor    

Connecting  Rods 

Cooling    

Crank  Shaft   

Cylinder  Construction 

Ignition   

Lubrication    . 


16 

39 
48 
83 
79 
51 
34 
26 
35 
42 
25 
35 
15 
39 
25 

19 
64 

40 

39 
79 
79 
82 
81 
82 
81 
81 
82 
81 


Pistons 

Specifications   of 

Starter    

Valves    .  .  . 


Page 
.  .  81 
.  .  7!) 
.  .  82 
. .  71) 


"I"-Head 17 

Idling if, 

Idling  Device 27,  33 

Ignition 9,  16,  36 

Delco    62 

Magneto    41 

Impeller 23 

Improper    Carburetion     33 

Induction,   Definition  of 35 

How  Accomplished   35-36 

Insulator   35 

Intake    Stroke    16 


Jet  . 


26 


"L"-Head    17 

Lean  Mixture,   Effects  of 34 

Liberty   Engine    51 

Angle  Between  Banks 53 

Army  Type 58 

Battery 64-66 

Cam  Shaft 55-57 

Carburetor    60 

Compression 58 

Connecting  Rods 58-59-60 

Cooling    55 

Crank  Shaft   58 

Cylinder    53-54-55 

Ignition   • 62 

Lubrication 55 

Model   B    63 

Navy  Type   58 

Reduction  of  Vibration 53 

Rocker  Arms   56 

Specifications  of    51 

Teardown 72-78 

Lines   of   Force 35 

Liquid   Bodies,   Law  of 27 

Lubrication,    Effects  of 24 

Methods  Used   24 

Reasons  for 24 

Magnet,  Electro  and  Permanent.  .  .    35 

Magnetism    35 

Magneto    41 

Armature 41 

Berling     41 

Bosch 41 

Dixie    42 

Polar  Inductor 42 

Shuttle 41 


94 


INDEX— 

Page 

Sparks  per  Revolution 42-43. 

Speed  of  Rotation 42-43 

Timing : 48 

Main  Jet   29 

Manif9lds    10,14 

Materials  of  Construction 86 

Mica 38 

Mixture    27 

Multi-cylinders     20 

Ohm  ...  35 

Oil  Duct  24 

Oil  Gauges  24 

Pumps  24 

Oil,  Use  of 25-26 

Changing  of  26 

Oscillatory  Current  38 

Discharge  39 

Overheating 22,  49,  90 

.  .  10,  14 


Piston,  Purpose  of 

Construction  of 87 

Piston  Displacement 14 

Piston  Pin 10 

Construction  of 87 

Piston  Ring    87 

Piston  Travel,   Measurement  of .  .  .  45 

Polar  Inductor 42 

Pop  Back    15 

Power  Stroke 16 

Power,  Unit  of 35 

Power  of  Curtiss    83 

of  Hispano-Suiza     79 

of  Liberty 51 

Power,   Increase   of 17,  19,  21,  30 

Pressure  Oiling   System    25 

Pressure  Relief  Valve    25 

Primary  Circuit 40 

Interruption   of    37,  44 

Primary   Coil    37 

Primary  Current 37 

Propeller  Alignment 19 

Drive    18-19 

Speeds    19 

Thrust    19 

Radiators 22 

Regulator,  Voltage 64 

Tyrrel 64 

Repairs 49,  88-89-90-91-92. 

Emergency  49 

Resistance 35 

Retarded  Spark,  Reason  for 47 

Effects  of 47 

Retarded  Timing  49 


Page 
Reversal   of '  Flux —;,  \  .V,  .*,}  <  ^.38,  42 

Rich   Mixture,  Effects   of 34 

Rocker  Arm 14-18 

Rotation,  Direction  of 46 

Determination  of 46 

Rotary  Pole   42 

Rotary  Shuttle 41 

Secondary  Circuit 40 

Secondary  Coil  37 

Current  37 

Shuttle 41 

Spark  Advance 47 

Spark  Plug 36 

Spark  Retard  47 

Stroke  14 

Sump,  Definition  of 14 

Dry 24 

"T"-Head  17 

Teardown,  Order  of,  for  Liberty..  72 

Details  of,  for  Liberty 73-78 

Thermo- Syphon  23 

Thrust  Bearing  .  . 14 

Timing  Gears 14 

Timing,  Magneto  . .  .  >. 48 

Valves  . . 44 

Trouble  Charts 88-92 

Twelve-Cylinder  Arrangement  ....  21 
Tyrrel  Regulator 64 

Vee  Type  Engine 21 

Valve  Action   44 

Valve  Clearance,  Definition 18 

Reason  for  and  effect  of 18 

Adjustment  of   46 

Valve  Closing 44 

Valves,  Exhaust  and  Intake 10-11 

Construction  of 87 

Grinding    18 

Location 17 

Movements  of 17 

Opening 44 

Operation,  Chart  of 44 

Springs    14 

Timing 44 

Reasons  for 45 

Venturi 29-3C 

Vibration    20,92 

Voltage  Regulator    64 

Volt    25 

Water  Circulation    22 

Water    Cooling    22 

Jackets 22 

Pumps    23 

Watt 35 


95 


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